Depletion of acyl-coenzyme A-binding protein affects sphingolipid synthesis and causes vesicle accumulation and membrane defects in Saccharomyces cerevisiae

Deletion of the yeast gene ACB1 encoding Acb1p, the yeast homologue of the acyl-CoA-binding protein (ACBP), resulted in a slower growing phenotype tha t adapted into a faster growing phenotype with a frequency >1:10(5). A cond itional knockout strain (Y700pGAL1-ACB1) with the ACB1 gene under control o f the GAL1 promoter exhibited an altered acyl-CoA profile with a threefold increase in the relative content of C18:0-CoA, without affecting total acyl -CoA level as previously reported for an adapted acb1 Delta strain. Depleti on of Acb1p did not affect the general phospholipid pattern, the rate of ph ospholipid synthesis, or the turnover of individual phospholipid classes, i ndicating that Acb1p is not required for general glycerolipid synthesis. In contrast, cells depleted for Acb1p showed a dramatically reduced content o f C26:0 in total fatty acids and the sphingolipid synthesis was reduced by 50-70%. The reduced incorporation of [H-3]myo-inositol into sphingolipids w as due to a reduced incorporation into inositol-phosphoceramide and mannose -inositol-phosphoceramide only, a pattern that is characteristic for cells with aberrant endoplasmic reticulum to Golgi transport. The plasma membrane of the Acb1p-depleted strain contained increased levels of inositol-phosph oceramide and mannose-inositol-phosphoceramide and lysophospholipids. Acb1p -depleted cells accumulated 50- to 60-nm vesicles, and autophagocytotic lik e bodies and showed strongly perturbed plasma membrane structures. The pres ent results strongly suggest that Acb1p plays an important role in fatty ac id elongation and membrane assembly and organization.