Structure-catalytic activity relationship in zebrafish RNases

Recently, four RNases from zebrafish (Danio rerio) have been identified and studied (ZF-RNase-1, -2, -3 and -4) [1-3]. Kazakou et al. [2], after an extensive survey of zebrafish DNA sequences, which indicated widespread polymorphism among the known ZF-RNase homologues, determined the X-ray structure of ZF-RNase-1 and -3 at basic pH. They also describe a polymorphic variant of the gene encoding ZF-RNase-2. More recently, we have proved that this variant is indeed a cell product by itself [4]. Here we report the X-ray structure of ZF-RNase-5 and that of ZF-RNase-1 at acidic and neutral pH. The structures have been directly compared with those described by Kazakou et al. [2] and with the structures of ZF-RNase-2 and -4, which have been obtained by homology modelling (Fig.1). The results have allowed to explain some differences in the catalytic activity of these proteins [4].