Polar residues mediate interhelical interactions in membrane proteins [electronic resource]

9780599984233

2000

1 online resource (210 p.)

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In this thesis, I examine the effect of polar residues in transmernbrane alpha-helices on the folding or association of integral membrane proteins. A transmembrane helix model system was designed to investigate influences on the assembly of transmembrane helices, in addition to the relative contributions and interdependence of interhelical polar and van der Waals packing interactions. Individual polar residues (Asn, Asp, Gln, Glu, Ser, Thr, Tyr, His and Lys) were placed within a poly-leucine or poly-valine sequence. A synthetic peptide and chimeric proteins comprising designed transmembrane sequences were successfully made and tested for specific association both in detergent and in biological membranes, compared to poly-leucine or poly-valine sequences without polar substitutions. Association of the transmembrane helix of human glycophorin A was used as a point of reference. The results demonstrate that the complementary packing interface of leucine zippers is insufficient to induce transmembrane helix association, but that inclusion of a polar residue may enhance the association dramatically. Residues that can be both hydrogen donors and acceptors, i.e. Asn, Asp, Gln, Glu and His, drive the association most strongly. Whereas leucine residues contribute little to the stability and specificity of the association, interfaces made of valine residues can compete with polar residues to mediate strong inter-molecular interactions, suggesting that great association specificity can be achieved by combining polar and van der Waals interactions. Strong interhelical polar interactions may constrain conformations of transmembrane helices and be regulated during protein conformational changes required for their biological functions. Furthermore, strong polar interactions within the hydrophobic environment of a membrane also imply a danger that unregulated and non-specific assembly of transmembrane helices might occur, leading to deadly biological consequences. Therefore, membrane proteins may fold to avoid exposure of strongly hydrogen bonding groups at their lipid exposed surfaces.

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English

July 12, 2011

Thesis (Ph.D.)--Yale University, 2000.

Yale University.