Pyridoxal phosphate (PLP)-dependent decarboxylase involved in the biosynthesis of amidated D-glucuronic acid structures found on the capsular polysaccharide (CPS) of C.jejuni. Catalyzes the decarboxylation of L-serine phosphate to ethanolamine phosphate. Less active with L-threonine phosphate. No activity with L-serine, L-threonine, L-aspartate or L-glutamate. H(+) + O-phospho-L-serine = CO2 + phosphoethanolamine kcat is 0.21 sec(-1) with L-serine phosphate as substrate. Capsule biogenesis; capsule polysaccharide biosynthesis. Belongs to the class-I pyridoxal-phosphate-dependent aminotransferase family.