Conservation of structure and function among histidine-containing phosphotransfer (HPt) domains as revealed by the crystal structure of YPD1

In Saccharomyces cerevisiae, the SLN1-YPD1-SSK1 phosphorelay system control s a downstream mitogen-activated protein (MAP) kinase in response to hypero smotic stress. YPD1 functions as a phospho-histidine protein intermediate w hich is required for phosphoryl group transfer from the sensor kinase SLN1 to the response regulator SSK1. In addition, YPD1 mediates phosphoryl trans fer from SLN1 to SKN7, the only other response regulator protein in yeast w hich plays a role in response to oxidative stress and cell wall biosynthesi s. The X-ray structure of YPD1 was solved at a resolution of 2.7 Angstrom by c onventional multiple isomorphous replacement with anomalous scattering. The tertiary structure of YPD1 consists of six a-helices and a short 3(10)-hel ix. A four-helix bundle comprises the central core of the molecule and cont ains the histidine residue that is phosphorylated. Structure-based comparis ons of YPD1 to other proteins having a similar function, such as the Escher ichia coli ArcB histidine-containing phosphotransfer (HPt) domain and the P 1 domain of the CheA kinase, revealed that the helical bundle and several s tructural features around the active-site histidine residue are conserved b etween the prokaryotic and eukaryotic kingdoms. Despite limited amino acid sequence homology among HPt domains, our analysi s of YPD1 as a prototypical family member, indicates that these phosphotran sfer domains are Likely to share a similar fold and common features with re gard to response regulator binding and mechanism for histidine-aspartate ph osphoryl transfer. (C) 1999 Academic Press.