Distribution and paralogue specificity of mammalian deSUMOylating enzymes

The covalent attachment of SUMO (small ubiquitin-like protein modifier) to target proteins results in modifications in their activity, binding interactions, localization or half-life. The reversal of this modification is catalysed by SENPs (SUMO-specific processing proteases). Mammals contain four SUMO paralogues and six SENP enzymes. In the present paper, we describe a systematic analysis of human SENPs, integrating estimates of relative selectivity for SUMO 1 and SUMO2, and kinetic measurements of recombinant C-terminal cSENPs (SENP catalytic domains). We first characterized the reaction of each endogenous SENP and cSENPs with HA SUMO-VS [HA (haemagglutinin)-tagged SUMO-vinyl sulfones], active-site-directed irreversible inhibitors of SENPs. We found that all cSENPs and endogenous SENP I react with both SUMO paralogues, whereas all other endogeneous SENPs in mammalian cells and tissues display high selectivity for SUMO2-VS. To obtain more quantitative data, the kinetic properties of purified cSENPs were determined using SUMO1- or SUMO2-AMC (7-amino-4-methylcoumarin) as substrate. All enzymes bind their respective substrates with high affinity. cSENP1 and cSENP2 process either SUMO substrate with similar affinity and catalytic efficiency; cSENP5 and cSENP6 show marked catalytic specificity for SUMO2 as measured by K(m) and k(cat) whereas cSENP7 works only on SUMO2. Compared with cSENPs, recombinant full-length SENP1 and SENP2 show differences in SUMO selectivity, indicating that paralogue specificity is influenced by the presence of the variable N-terminal domain of each SENP. Our data suggest that SUMO2 metabolism is more dynamic than that of SUMO1 since most SENPs display a marked preference for SUMO2.