Rescuing Glycine

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Science  04 Nov 2005:
Vol. 310, Issue 5749, pp. 747
DOI: 10.1126/science.310.5749.747c

The two ways to achieve structural stability of an integral membrane protein are to bundle α helices together, as in lactose permease, and to curl a β sheet (comprised of individual β strands) into a barrel, as exemplified in the family of porins. The β-barrel proteins are found in the outer membrane of bacteria and of organelles (mitochondria and chloroplasts) thought to have a bacterial heritage.

Jackups and Liang have systematically analyzed the small, but growing, data set of three-dimensional structures of β-barrel membrane proteins in order to establish the propensities of interstrand amino acid neighbors. These values have current application to improving sequence-based alignments across proteins as well as the register between β strands within proteins. In addition, motifs and antimotifs of pairs of amino acids may find application in future studies of β-barrel membrane protein biogenesis (folding, translocation, and insertion). One such motif, originally identified in soluble β-barrel proteins, is termed aromatic rescue of glycine. The curvature of the inner (and often solvent-exposed) surface of a β barrel is facilitated by glycine residues, and the energetically unfavorable exposure of the peptide backbone can be mitigated by covering the glycine with an aromatic side chain, such as is found in tyrosine and phenylalanine, from a neighboring stave of the barrel. — GJC

J. Mol. Biol. 10.1016/j.jmb.2005.09.094 (2005).

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