HOMOLOGOUS DNA PAIRING DOMAIN PEPTIDES OF RECA PROTEIN - INTRINSIC PROPENSITY TO FORM BETA-STRUCTURES AND FILAMENTS

The 20 amino acid residue peptides derived from RecA loop L2 have been shown to be the pairing domain of RecA. The peptides bind to ss- and dsDNA, unstack ssDNA, and pair the ssDNA to its homologous target in a duplex DNA. As shown by circular dichroism, upon binding to DNA the d isordered peptides adopt a beta-structure conformation. Here we show t hat the conformational change of the peptide from random coil to beta- structure is important in binding ss- and dsDNA. The beta-structure in the DNA pairing peptides can be induced by many environmental conditi ons such as high pH, high concentration, and non-micellar sodium dodec yl sulfate (6 mM). This behavior indicates an intrinsic property of th ese peptides to form a beta-structure. A beta-structure model for the loop L2 of RecA protein when bound to DNA is thus proposed. The fact t hat aromatic residues at the central position 203 strongly modulate th e peptide binding to DNA and subsequent biochemical activities can be accounted for by the direct effect of the aromatic amino acids on the peptide conformational change. The DNA-pairing domain of RecA visualiz ed by electron microscopy self-assembles into a filamentous structure Like RecA. The relevance of such a peptide filamentous structure to th e structure of RecA when bound to DNA is discussed. (C) 1998 Academic Press Limited.