An Investigation into the Function and Regulation of GAPDH in Staphylococcus aureus

Staphylococcus aureus is an important pathogen of both humans and animals. With the growing spread of MRSA strains in clinical environments and the wider community, it is imperative that we understand the basic physiology of this species to find new antimicrobial or vaccine targets. This project focuses on the function and regulation of glyceraldehyde-3-phosphate dehydrogenase, or GAPDH, an essential component of glucose metabolism. S. aureus contains two GAPDH homologues; GapA, a known GAPDH protein and GapB, the function of which is undefined. Using a number of complementary approaches we have shown that GapA and GapB have reciprocal functions during glucose metabolism, and that both homologues are required during infection. We have also identified novel “moonlighting” roles for both GapA and GapB and shown that both genes are regulated by divalent metal ions. Interestingly iron regulation of gapA is strain variable at the transcriptional level due to sequence variation between strains, and appears to involve a S. aureus repeat (STAR) element locus. To our knowledge this is the first indication that these repeat elements are functional. STAR elements are found across the S. aureus genome, and the number of repeats at each locus is variable between strains. Surprisingly the three STAR loci (gapR, hprK and orf0733) analysed are highly conserved and maintained in the S. aureus genome at a level similar to that of MLST loci which suggests that they may have an important function, although transcriptional analysis failed to identify a correlation between repeat number and transcript levels. However transcriptional analysis did demonstrate that a number of STAR and non-STAR associated loci in S. aureus, including housekeeping genes involved in central metabolism, known transcriptional regulators and virulence factors show strain variable levels of expression, which may play a role in the significant adaptability of S. aureus.