Exploring the biological functions of the novel lipoamidase SIRT4

Sirtuins (SIRTs) are a critical family of seven mammalian nicotinamide adenine dinucleotide (NAD+)-dependent enzymes which govern genome regulation, metabolism, and aging. SIRTs display widespread subcellular distributions; SIRT1, SIRT6, and SIRT7 are nuclear, SIRT2 is predominantly cytoplasmic, and SIRTs3-5 are mitochondrial. Despite all SIRTs containing a conserved deacetylase domain, only SIRTs1-3 show robust deacetylation activity. Importantly, knock-down of SIRT expression, increases HCMV titer following infection, leading to their classification as viral restriction factors. However, the precise host mechanisms of action remain unknown.

We recently discovered SIRT4 is the first mammalian cellular lipoamidase, and can hydrolyse lipoyl- and biotinyl-lysine modifications far more efficiently than acetyl-lysine. Mitochondrial pyruvate dehydrogenase complex (PDH), which converts pyruvate to acetyl-CoA, is a biological substrate, and SIRT4 can enzymatically hydrolyze the lipoamide cofactors from the E2 component dihydrolipoyllysine acetyltransferase (DLAT) to diminish overall PDH activity.

This project investigates the following questions:
(1) Can SIRT4 hydrolyze the lipoamide from other dehydrogenase complexes?
(2) Which biotin-modified mitochondrial proteins are substrates of SIRT4?
(3) Does HCMV have a protein that inhibits SIRT4 during infection?