Discovery of a cardiolipin synthase utilizing phosphatidylethanolamine and phosphatidylglycerol as substrates

摘要

Depending on growth phase and culture conditions, cardiolipin (CL) makes up 5-15% of the phospholipids in Escherichia co//with the remainder being primarily phosphatidylethanolamine (PE) and phosphatidylglycerol (PG). In E. coli, the c/s and ybhO genes (renamed dsA and dsB. respectively) each encode a CL synthase (CIs) that catalyzes the condensation of two PG molecules to form CL and glycerol. However, a AclsAB mutant still makes CL in the stationary phase, indicating the existence of additional CIs. We identified a third CIs encoded by ymdC (renamed c/sC). CIsC has sequence homology with CIsA and CIsB, which all belong to the phospholipase D superfamily. The AdsABC mutant lacks detectible CL regardless of growth phase or growth conditions. CL can be restored to near wild-type levels in stationary phase in the triple mutant by expressing either dsA or dsB. Expression of dsC alone resulted in a low level of CL in the stationary phase, which increased to near wild-type levels by coexpression of its neighboring gene, ymdB. CL synthesis by all CIs is increased with increasing medium osmolarity during logarithmic growth and in stationary phase. However, only CIsA contributes detectible levels of CL at low osmolarity during logarithmic growth. Mutation of the putative catalytic motif of CIsC prevents CL formation. Unlike eukaryotic CIs (that use PG and CDP-diacylglycerol as substrates) or CIsA, the combined YmdB-CIsC used PE as the phosphatidyl donor to PG to form CL, which demonstrates a third and unique mode for CL synthesis.