Inverse protein folding by the residue pair preference profile method: estimating the correctness of alignments of structurally compatible sequences

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Abstract
The residue pair preference profile (R3P) method is an inverse folding method that combines environmental profiles and pair preference profiles. The method uses statistical preferences for residue pairs which score the likelihood of finding a profiled residue to be paired with a residue within its local environment. All pairs are characterized by their dihedral angles, secondary structure and number of neighboring residues as a function of residue type. Each residue pair preference is expressed for all 20 amino acids of the profiled residue and is weighted by the compatibility of the environment residue with its own local environment. The R3P method produces an initial profile-sequence alignment which is then refined by converting the initial profile into a profile of a target sequence threaded into the structure of the initial profile. We have tested this method by evaluating alignments of sequences with known 3-D structures using structural superposition alignments as reference. R3P-sequence alignments are > or = 50% correct on average for sequences whose 3-D structure pairs superimpose with an r.m.s. deviation of < or = 1.97 A. The average improvement in correctness during this iterative refinement is 14%. The R3P-sequence alignments are compared with sequence-sequence and 3-D profile-sequence alignments. When all three methods are combined, on average > or = 50% of the alignments are correct for pairs of 3-D structures that superimpose within 2.12 A. A 3-D model of HisA is predicted with the combined method.

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