Surface study of apoB1694–1880, a sequence that can anchor apoB to lipoproteins and make it nonexchangeable

Apolipoprotein B (apoB) is a nonexchangeable apolipoprotein. During lipoprotein assembly, it recruits phospholipids and triacylglycerols (TAG) into TAG-rich lipoprotein particles. It remains bound to secreted lipoproteins during lipid metabolism in plasma. The β1 region (residues 827–1880) of apoB has a high amphipathic β strand (AβS) content and is proposed to be one region anchoring apoB to lipoproteins. The AβS-rich region between apoB37 and apoB41 (residues 1694–1880) was cloned, expressed, and purified. The interfacial properties were studied at the triolein/water (TO/W) and air/water (A/W) interfaces. ApoB[37–41] is surface-active and adsorbs to the TO/W interface. After adsorption the unbound apoB[37–41] was removed from the aqueous phase. Adsorbed apoB[37–41] did not desorb and could not be forced off by increasing the surface pressure up to 23 mN/m. ApoB[37–41] adsorbed on the TO/W interface was completely elastic when compressed and expanded by ±13% of its area. On an A/W interface, the apoB[37–41] monolayer became solid when compressed to 4 mN/m pressure indicating extended β-sheet formation. It could be reversibly compressed and expanded between low pressure and its collapse pressure (35 mN/m). Our studies confirm that the AβS structure of apoB[37–41] is a lipid-binding motif that can irreversibly anchor apoB to lipoproteins. Apolipoprotein B (apoB) is a nonexchangeable apolipoprotein. During lipoprotein assembly, it recruits phospholipids and triacylglycerols (TAG) into TAG-rich lipoprotein particles. It remains bound to secreted lipoproteins during lipid metabolism in plasma. The β1 region (residues 827–1880) of apoB has a high amphipathic β strand (AβS) content and is proposed to be one region anchoring apoB to lipoproteins. The AβS-rich region between apoB37 and apoB41 (residues 1694–1880) was cloned, expressed, and purified. The interfacial properties were studied at the triolein/water (TO/W) and air/water (A/W) interfaces. ApoB[37–41] is surface-active and adsorbs to the TO/W interface. After adsorption the unbound apoB[37–41] was removed from the aqueous phase. Adsorbed apoB[37–41] did not desorb and could not be forced off by increasing the surface pressure up to 23 mN/m. ApoB[37–41] adsorbed on the TO/W interface was completely elastic when compressed and expanded by ±13% of its area. On an A/W interface, the apoB[37–41] monolayer became solid when compressed to 4 mN/m pressure indicating extended β-sheet formation. It could be reversibly compressed and expanded between low pressure and its collapse pressure (35 mN/m). Our studies confirm that the AβS structure of apoB[37–41] is a lipid-binding motif that can irreversibly anchor apoB to lipoproteins. Apolipoprotein B (apoB) is a large protein (4536 residues) that plays an essential role in the formation of triacylglycerol (TAG)-rich lipoproteins by the intestine, as chylomicrons, or by the liver, as VLDL (1Kane J.P. Havel R.J. Disorders of the biogenesis and secretion of lipoproteins containing the B apolipoproteins.in: Scriver C.R. Beaudet A.L. Valle D. The Metabolic and Molecular Bases of Inherited Disease. McGraw–Hill, New York2001: 2717-2752Google Scholar). The N-terminal 48% of apoB (apoB48) in the intestine and the full-length apoB (apoB100) in the liver play fundamental roles in the assembly and into a is secreted and the or liver the to by lipoprotein to as a of or and lipid is and a of the of that irreversibly to lipid (1Kane J.P. Havel R.J. Disorders of the biogenesis and secretion of lipoproteins containing the B apolipoproteins.in: Scriver C.R. Beaudet A.L. Valle D. The Metabolic and Molecular Bases of Inherited Disease. McGraw–Hill, New York2001: 2717-2752Google R.J. J.P. structure and metabolism of Scriver C.R. Beaudet A.L. Valle D. The Metabolic and Molecular Bases of Inherited Disease. McGraw–Hill, New York2001: Scholar). a the of in and in and and as in The to of and to lipid Scholar). and a large region that has to anchor to particles. is the nonexchangeable it remains the from the it is in the liver or intestine it is removed and (1Kane J.P. Havel R.J. Disorders of the biogenesis and secretion of lipoproteins containing the B apolipoproteins.in: Scriver C.R. Beaudet A.L. Valle D. The Metabolic and Molecular Bases of Inherited Disease. McGraw–Hill, New York2001: 2717-2752Google R.J. J.P. structure and metabolism of Scriver C.R. Beaudet A.L. Valle D. The Metabolic and Molecular Bases of Inherited Disease. McGraw–Hill, New York2001: Scholar). between lipoproteins as and in the plasma. has to to and to in to in surface pressure Apolipoprotein B is at a triolein/water a lipoprotein Scholar). the be completely from the triolein/water (TO/W) interface, of the to desorb as surface pressure is and to as the pressure is Apolipoprotein B is at a triolein/water a lipoprotein Scholar). studies that a amphipathic β strand (AβS) or a amphipathic β from to β region of irreversibly to air/water and TO/W the interfacial properties of amphipathic β strand of B at Scholar). to high surface pressure not the from the interface AβS an completely elastic interface at the and TO/W of structure and studies on AβS it was that the β1 (residues 827–1880) and (residues of the that apoB from the it is Apolipoprotein B is at a triolein/water a lipoprotein properties of amphipathic β strand of B at J.P. of in low D. The region of is a amphipathic and and assembly of Scholar). of has the β1 anchoring on a of structure the of apoB from to (residues was to be a amphipathic β in and D. The region of is a amphipathic and and assembly of Scholar). It is that the region between and can the formation of lipoprotein that phospholipids and in of of B in that the of B has a on the of the secreted Apolipoprotein B lipoprotein Apolipoprotein B low lipoprotein that lipid of lipid is by in the N-terminal of of the lipoprotein of J.P. Apolipoprotein lipoprotein lipid of the lipoprotein J.P. of lipoprotein containing the lipoprotein J.P. protein is not the of lipoprotein assembly in Scholar). containing low of the protein lipoproteins secreted from N-terminal of apoB an in secretion when the secreted apoB is the N-terminal The of from in secreted to in and to in of lipid is by in the N-terminal of Scholar). and a by of the β1 region of apoB to the of by as the the that AβS to that an from to be in AβS and the secretion of has properties to the properties of amphipathic β strand of B at Scholar). cloned, expressed, and a from the β region between apoB37 and 1694–1880) and studied its at the and A/W interfaces. region AβS of and J.P. of in low D. The region of is a amphipathic and and assembly of Scholar). The region is at β of that it is irreversibly bound to the it be off by up to and it is completely a anchoring region of apoB to to the from that AβS of apoB to anchor and to lipoproteins. region from to D. of lipid by the The assembly and secretion of low lipoproteins in and lipid-binding of the N-terminal of The N-terminal of apoB and irreversibly to low interfacial properties of and at the air/water and from the of lipoproteins in of of was containing and the of apoB of a in a of the the was and and to the were on and was and a was and to of and at to of The were by and to of and to of The was to of and to an of was to a of and the was at The were by and the was at the the were on and in of containing of a and of The was and the containing the apoB protein were by were in of and After the was a of The was into a and at and at was from the of and of and the protein was and The is in were between and on an at in containing the was by the of and and by studies were on at low as into a protein Scholar). The interfacial of the TO/W interface in the of apoB[37–41] in the aqueous was an The the of Scholar). of apoB[37–41] in was to the aqueous to a from to and apoB[37–41] is was in the aqueous and the interfacial was it an The surface pressure was from of the interface of the interface were at in a the were by protein was from interfacial was mN/m. were of was to to the surface the aqueous containing the by the aqueous from the surface and the of the was removed of the in the aqueous phase. into the aqueous during or surface and an the was compressed by the by as as or as as the was by The in the surface and in a to to a and an surface is the surface of mN/m). The was and was it the of of the from the surface was Apolipoprotein B is at a triolein/water a lipoprotein Scholar). the surface was expanded by increasing the to the and was and from the an not at a low the compressed surface is to the the in surface on is an aqueous of or the has of the in the aqueous to to the The of be to the of the adsorption from the aqueous the not the to on After the has removed from the aqueous could has the surface to a the and at the high in the of in the aqueous can on the was not the to to the and surface to the at high pressure the is compressed into a and the surface to into a the a and on to or were at the The was at and an The and were as the the the interfacial the between and and the and the were of adsorbed at air/water and D. at properties of by Scholar). was in a containing of After the was The was compressed at a of to a The compressed was and was at a of to the After at the was at a were at and surface in of and and were After the the was and was of apoB[37–41] in was on a surface of at to the of and of at the Scholar). of apoB[37–41] were compressed at mN/m on a of a surface and were the of the of the apoB[37–41] the monolayer was compressed to or and expanded at mN/m to a The of the monolayer or solid was by on the a of and the of properties of of of Scholar). the the and in the and in the solid The apoB[37–41] was up to at low and in as were in The was in and the was as a of The of to the of the β structure between and the at was the of of were structure is to the of protein from as studies were at low of or and at of the protein is and of from to in the aqueous were The to mN/m and mN/m the was were at from to the was mN/m. was between and in were at mN/m). of the were from as a adsorption of apoB[37–41] at TO/W interface and the and of the interface an The in the aqueous is the the that apoB[37–41] is surface-active and the surface of the TO/W interface to an in The an of the of and of the interface apoB[37–41] in the aqueous phase. After an the was compressed by the by and 4 and at a to was the the did not to The was expanded to and the or to the the from to mN/m and between and mN/m that compressed in was at the compressed that was of the from the the surface was expanded to the of to the on the by a in to as the and 4 from the to mN/m and mN/m and to mN/m and the compressed On the was to and to mN/m and were to the the at were not at 4 of the and to The from that was mN/m. apoB[37–41] adsorbs the TO/W interface, it be from the interface, a of the is the mN/m. that large a large in as low as 4 mN/m to or the was to was to that from the During the was a in of by a of the of an aqueous containing protein to of the surface to by the and at of the interfacial and the apoB[37–41] at TO/W interface and the and and The and was the an was in The of apoB[37–41] was in the aqueous phase. the in the was compressed by the by and 4 to in and to the The and was the an and the was in The of apoB[37–41] was in the aqueous After the was as the in the The was the the was compressed by the by and to in and to the the was to the by the at a of the was the was as the in the the was to at a of and were the were at an of the the and the and of the interface was and large were the the aqueous containing apoB[37–41] was by at 4 a on and a on at 4 and from to a in of the to of is the and the in is as the 4 is a of on of to 4 mN/m and a is to a mN/m). of on an a to a that the forced off of the interface, and when the interface was a of that on in a is into the or the the large to the was to to the of mN/m. that the was from to that of the adsorbed was from the surface by the was in indicating that the did not desorb during to the a increasing of to mN/m. that of to mN/m is from the The and to and the surface was compressed by the from to and in the and or or a the compressed the surface was expanded to the to the or or a and to the the apoB[37–41] in the aqueous the bound apoB[37–41] be off the surface by The in the in the the of at The was to from and at that not during After a a was to the of the to The was that bound to the interface. of of and were and the the as was and the were the not that the is a in from to not its surface a of the was at that a could be the in is in the phase. were at of and The in of the compressed is the that was in the when of up to and were a at 4 and at that is a the of protein from the surface at between and 4 in The to is 23 mN/m to of mN/m and The and the and the adsorption and the was in The of apoB[37–41] in the aqueous was was as the in the the was compressed by the by and at a of to After the compressed was the was by increasing the to the at the the was as the in the the from 23 mN/m to mN/m. The of the the the in of from in the The in The of and 4 on the on and from or the at a on that on it that the the the the in on The is up to a of that when the to be from the to high pressure to of the the was to a surface pressure of mN/m and a was The during the indicating that the did not the surface at high the was to the the to the indicating that the surface was in its compressed the in of and from the in from and 4 and was in the indicating an elastic from and and of and 4 indicating of protein at the the of the at the interface large the surface was to and was to was a of the from 23 to that the compressed that was from the surface the that the compressed or that the monolayer at of apoB[37–41] at and were and a of the of apoB[37–41] were from the at and 4 from to The of apoB[37–41] in the aqueous was The in the and the is indicating a elastic is of of the apoB[37–41] between the surface and the during the mN/m. is that the apoB[37–41] not desorb bound to the TO/W interface. of and the of the and of and and and in studies Apolipoprotein B is at a triolein/water a lipoprotein properties of amphipathic β strand of B at D. properties of an amphipathic of at air/water and D. The N-terminal and of at the triolein/water apoB[37–41] a elastic from mN/m pressure of apoB[37–41] at the TO/W interface from the and and at a was at 4 and from to The of apoB[37–41] in aqueous was After and at the a was at and from to ApoB[37–41] was in the aqueous and was interfacial properties of apoB[37–41] at TO/W in the was to at the the the were between and and by the were in at or The of apoB[37–41] in the aqueous was interfacial of a between and elastic the of elastic the of the was to at the the the were between and and by in a the were in at or The of apoB[37–41] in the aqueous was interfacial of a between and elastic the of elastic the of After the of the apoB[37–41] TO/W interface were at and a of the of apoB[37–41] TO/W interface, were from at and 4 from to was apoB[37–41] in the aqueous phase. The in The at and indicating a elastic surface and to in and to that the in the aqueous in the surface to the and the when compressed to of apoB[37–41] at the A/W interface. apoB[37–41] was on a The was in to of the on the was on the surface to the of the monolayer by the off at apoB[37–41] that apoB[37–41] is on the of the of the to the a of The and at mN/m apoB[37–41] has an of The monolayer of apoB[37–41] was can on the when was the monolayer was and can the surface became when was between and 4 and the monolayer was solid when was 4 and the up and of apoB[37–41] at the A/W interface. ApoB[37–41] in at was on a at The monolayer was compressed at mN/m to the at and at mN/m The of the surface as a of is The monolayer was compressed and expanded at mN/m from to mN/m from to mN/m and from to mN/m The compressed to mN/m the collapse of that the has a the indicating The was studied by from and from to mN/m and to the the up and were indicating the monolayer was at the monolayer was solid 4 mN/m. from to mN/m and to the the up and were indicating the monolayer was in as when from to mN/m the collapse pressure of and to the the up and were not indicating the monolayer was not the collapse The of apoB[37–41] on from mN/m was that of the ApoB[37–41] of a amphipathic β-sheet can be bound into a solid monolayer reversibly compressed and expanded the collapse the amphipathic β-sheet structure is to as the fundamental the nonexchangeable lipid motif of is a nonexchangeable apolipoprotein. The of apoB lipid and The apoB to to TAG-rich lipoprotein and to be during lipid metabolism (1Kane J.P. Havel R.J. Disorders of the biogenesis and secretion of lipoproteins containing the B apolipoproteins.in: Scriver C.R. Beaudet A.L. Valle D. The Metabolic and Molecular Bases of Inherited Disease. McGraw–Hill, New York2001: 2717-2752Google R.J. J.P. structure and metabolism of Scriver C.R. Beaudet A.L. Valle D. The Metabolic and Molecular Bases of Inherited Disease. McGraw–Hill, New York2001: from VLDL to The the of apoB on lipoprotein of and to and lipoproteins and in of low lipoproteins of of from in in lipid and in Molecular of and lipoprotein surface and Scholar). is in AβS and amphipathic and can be into J.P. of in low of the and of J.P. has a structure of amphipathic amphipathic by the Scholar). The from the N-terminal up to is an and β structure region the to and The of lipid in a structure of a the assembly and secretion of J.P. N-terminal of B has to and a of lipoprotein D. of lipid by the Scholar). can be secreted lipid of of B in that the of B has a on the of the secreted Apolipoprotein B lipoprotein and as an in The assembly and secretion of low lipoproteins in Scholar). as as can be secreted the of apoB has was to to phospholipids and lipid-binding of the N-terminal of The N-terminal of apoB and irreversibly to low and interfacial properties of and at the air/water and Scholar). and to and interfacial properties of the lipoprotein of Scholar). to the N-terminal β not to of apoB as properties of amphipathic β strand of B at J.P. of in low D. The region of is a amphipathic and and assembly of of of B in that the of B has a on the of the secreted Apolipoprotein B lipoprotein Apolipoprotein B low lipoprotein that lipid of lipid is by in the N-terminal of of the lipoprotein of to phospholipids and of the region in D. in the N-terminal region of of lipoproteins containing the N-terminal of Scholar). The region of to in a properties of a from B (residues Scholar). the N-terminal of apoB during in the in it to be secreted a of lipid or as a The assembly and secretion of low lipoproteins in is of the lipoprotein of Scholar). The between and apoB41 is up of amphipathic β structure and plays an essential role in to TAG-rich lipoprotein of of B in that the of B has a on the of the secreted Apolipoprotein B lipoprotein Apolipoprotein B low lipoprotein that lipid of lipid is by in the N-terminal of of the lipoprotein of J.P. Apolipoprotein lipoprotein lipid of the lipoprotein J.P. of lipoprotein containing the lipoprotein J.P. protein is not the of lipoprotein assembly in Scholar). The region from to apoB41 has a to to lipoproteins of lipid is by in the N-terminal of Scholar). The from to and the from to the of apoB in and of the of J.P. of in low Scholar). The from to is in the J.P. of in low Scholar). one to on studies of of low Scholar). It has that AβS and structure the lipid properties of apoB AβS anchor apoB on lipid Apolipoprotein B is at a triolein/water a lipoprotein properties of amphipathic β strand of B at J.P. of in low Scholar). and that the region between and at AβS of or and to was D. The region of is a amphipathic and and assembly of Scholar). the of by J.P. of in low Scholar). at the surface properties of AβS and properties of amphipathic β strand of B at the AβS and structure between and has one β strand of and a of a β to a amphipathic of the AβS to and A/W to the interfacial be off the surface when the surface is compressed by can a pressure of mN/m and can a pressure of mN/m at the TO/W interface pressure could not be of the completely elastic at when the surface is compressed and expanded by in area. on structure properties of amphipathic β strand of B at J.P. of in low D. The region of is a amphipathic and and assembly of of the and of apoB[37–41] amphipathic β of and or apoB[37–41] a β-sheet apoB[37–41] lipid at the TO/W interface. It the surface and the surface compressed by is a in and a on a of the off a of mN/m and on of the bound apoB[37–41] can be compressed by up to in to a surface pressure of 23 mN/m is the interfacial of and at the TO/W interface properties of amphipathic β strand of B at Scholar). the of apoB[37–41] to the from the AβS ApoB[37–41] is completely elastic on the surface when the surface was compressed and expanded in and that apoB[37–41] to the bound to the and the in the aqueous the is the bound apoB[37–41] not the bound remains bound up to a in of and of is elastic on the surface apoB[37–41] to the interface, the a β-sheet structure between as by the formation of a solid interface at the A/W interface at low pressure 4 compressed to a high pressure and to an of its at a of the is that the is off into the aqueous that a in of a surface into a structure is in the be to to full-length apoB can be compressed to mN/m a in of and the surface of the on to from the of from the large of and J.P. of in low Scholar). The of apoB is at and of apoB by Apolipoprotein B is at a triolein/water a lipoprotein that of the can be The of apoB[37–41] of mN/m is and a low of the that can reversibly is and to full-length on AβS at A/W interface a β-sheet structure on the surface D. properties of between and β-sheet amphipathic at and of of β-sheet at of β-sheet Scholar). on a of β-sheet the by that monolayer at A/W interface of β-sheet at Scholar). on the of the and the by in of β-sheet Scholar). off at by a and at mN/m an of The is mN/m the area. compressed on a during It was that the β-sheet monolayer a and at the interface of β-sheet Scholar). the and and the of the on the interface, is the of the in the interface, and is the between a β-sheet of a and a of is a β-sheet of The in that the assembly can be compressed up to the and on the β-sheet structure can be to its the between the β the during the and the from at mN/m to at mN/m. the of the to the surface is by The that the were the the to the β-sheet to of the surface when compressed to a pressure the of β-sheet can of the of the surface when ApoB[37–41] a of the β-sheet structure at the A/W interface. It off at by a in the and at mN/m an of and that apoB[37–41] is on the surface at its of The monolayer became solid when the pressure was 4 and it can be reversibly compressed and expanded the collapse pressure the collapse the monolayer an and to the of β-sheet Scholar). on the of the of the monolayer amphipathic at and of the of at the in the is is to of β-sheet Scholar). the apoB[37–41] monolayer β-sheet structure of a solid on the surface and the lipid of AβS the and of structure is to to the of apoB Apolipoprotein B is at a triolein/water a lipoprotein properties of amphipathic β strand of B at D. The interfacial properties of and an amphipathic of at the triolein/water Scholar). The of from the of the in and of apoB D. The interfacial properties of and an amphipathic of at the triolein/water Scholar). to TO/W interface and the interface On it from the interface an interfacial pressure of and when the surface is expanded to the and the pressure is the It is that the of apoB when compressed and The of apoB to the pressure in the of apoB when apoB was the A/W interface Apolipoprotein B is at a triolein/water a lipoprotein Scholar). off at the pressure to a at 23 mN/m the of by a to mN/m the of and the pressure to mN/m an monolayer low pressure the of apoB was between extended to the between and at the pressure to 23 mN/m the of that of the were off the AβS bound to the is the of J.P. of in low that the by AβS in β1 and of is The region between and be the of the of the and the elastic of The in of apoB from at to at mN/m is the AβS of β1 and bound on the A/W the that AβS in apoB can be compressed to is the that from the β region of apoB can be compressed on a TO/W interface to properties of amphipathic β strand of B at apoB[37–41] can be compressed to collapse at A/W interface. at pressure AβS on the and the of AβS is the at the TAG-rich lipoprotein secreted into the as or VLDL to the the is up as a or an apoB remains on the lipoprotein the lipoprotein metabolism in in and the surface pressure increasing surface-active to the surface or a the of apoB and is by in of its surface lipoproteins and in of low lipoproteins of of from in in lipid and in Molecular of and lipoprotein surface and Scholar). It is to that the TAG-rich lipoprotein a low surface pressure and to to the in lipoprotein on the surface and the surface and and the the surface pressure off of the bound and apoB amphipathic desorb and the of removed by the surface pressure that in surface pressure of to a or to and the and elastic of AβS structure be a during lipoprotein assembly in the that in AβS is a that irreversibly to and is of the anchor of apoB that recruits during lipoprotein formation. The

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