SpkH (Sll00 05) from Synechocystis sp. PCC 6803 is an active Mn2+- dependent Ser kinase

Twelve genes for the potential serine-threonine protein kinases (STPKs) have been annotated in the genome of Synechocystis sp. PCC 6803. Based on similarities and distinctive domain organization, they were divided into two clusters: serine/threonine-protein N2-like kinases (PKN2-type) and "activity of bc1 complex" kinases (ABC1-type). While the activity of the PKN2-type kinases have been demonstrated, no ABC1-type kinases activity have hitherto been reported. In this study, a recombinant protein previ-ously annotated as a potential STPK of ABC1-type (SpkH, Sll00 05) was expressed and purified to ho-mogeneity. We demonstrated SpkH phosphorylating activity and substrate preference for casein in in vitro assays using [g-32P]ATP. Detailed analyses of activity showed that Mn2+ had the strongest acti-vation effect. The activity of SpkH was significantly inhibited by heparin and spermine, but not by staurosporine. By means of semi-quantitative mass-spectrometric detection of phosphopeptides, we identified a consensus motif recognized by this kinase -X1X2pSX3E. Thus, we first report here that SpkH of Synechocystis represents a true active serine protein kinase, which shares the properties of casein kinases according to its substrate specificity and sensitivity to some activity effectors. & COPY; 2023 Elsevier B.V. and Societe Francaise de Biochimie et Biologie Moleculaire (SFBBM). All rights reserved.