Golgi serine/threonine protein kinase that phosphorylates secretory pathway proteins within Ser-x-Glu/pSer motifs. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Resides in the Golgi apparatus membrane and is secreted following propeptide cleavage. In embryos, prominently expressed in midline glia, salivary gland, intestine and dorsal vessel (heart). Not associated with biomineralization. Belongs to the FAM20 family.