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Abstract:
The frequency of occurrence of nearest neighbour residue pairs on adjacent antiparallel (βA) and parallel (βP) strands is obtained from 30 known protein structures. The specificity of interstrand recognition due to such pairing as a factor in the folding of β-sheets is studied by statistical methods. Residues of sufficiently high count for statistical analysis are treated individually while the rest are combined into small groups of similar size, polarity, and/or genetic exchangeability. The hypothesis of specific recognition between individuals and small groups is contrasted with the alternative hypothesis of non-specific recognition between broad classes (hydrophobia, neutral, polar) of residues. A χ2 test of pair correlations favours specific recognition against non-specific recognition with a high level of confidence. The largest and most significant correlations are: Ser/Thr (1.9 ± 0.3), Ile/Val (1.7 ± 0.3) and Lys-Arg/Asp-Gln (1.8 ± 0.3) in βA, and Ile/Leu (1.9 ± 0.4) in βP. The pair Gly/Gly never occurs in any β-sheet. The specific residue-pair correlations derived here may be useful in statistical prediction methods of protein tertiary structure.
