Enhancement of transport-dependent decarboxylation of phosphatidylserine by S100B protein in permeabilized Chinese hamster ovary cells

Phosphatidylethanolamine synthesis through the phosphatidylserine (PtdSer) decarboxylation pathway requires PtdSer transport from the endoplasmic reti culum or mitochondrial-associated membrane to the mitochondrial inner membr ane in mammalian cells. The transport-dependent PtdSer decarboxylation in p ermeabilized Chinese hamster ovary (CHO) cells was enhanced by cytosolic fa ctors from bovine brain. A cytosolic protein factor exhibiting this enhanci ng activity was purified, and its amino acid sequence was partially determi ned. The sequence was identical to part of the amino acid sequence of an EF -hand type calcium-binding protein, S100B. A His(6)-tagged recombinant CHO S100B protein was able to remarkably enhance the transport-dependent PtdSer decarboxylation in permeabilized CHO cells. Under the standard assay condi tions for PtdSer decarboxylase, the recombinant S100B protein did not stimu late PtdSer decarboxylase activity and exhibited no PtdSer decarboxylase ac tivity. These results implicated the S100B protein in the transport of PtdS er to the mitochondrial inner membrane.