Curation Notes: act (B9U6P4) in Variovorax paradoxus

Overview

UniProt ID: B9U6P4 (B9U6P4_VARPD, 398 aa)
Gene symbol / locus tag: act (VPARA_05450, Act(TBEA6), KLN58430.1)
Organism: Variovorax paradoxus strain TBEA6 (NCBITaxon:34073)
Function: Cytosolic homodimeric succinyl-CoA:3-sulfinopropionate CoA-transferase (EC 2.8.3.-, family III CoA-transferase Pfam:PF02515 / InterPro:IPR003673).

Direct purification and steady-state kinetics (PMID:23772073): Schürmann et al. 2013 (PMID:23772073) heterologously expressed and purified Act(TBEA6) (B9U6P4) as a 96 ± 3 kDa homodimer. It transfers CoA from succinyl-CoA ($V_{\max} = 44.6\ \mu\text{mol min}^{-1}\text{ mg}^{-1}$, $K_m = 0.08\ \text{mM}$, $k_{\text{cat}} = 36.0\ \text{s}^{-1}$), itaconyl-CoA, or glutaryl-CoA to 3-sulfinopropionate ($V_{\max} = 46.8\ \mu\text{mol min}^{-1}\text{ mg}^{-1}$, $K_m = 5.9\ \text{mM}$, $k_{\text{cat}} = 37.7\ \text{s}^{-1}$) to produce 3-sulfinopropanoyl-CoA (3SP-CoA).
Operon context and polar effect on acd (B9U6P5): Bruland et al. 2009 (PMID:19001372) isolated a Tn5::mob mutant in act that accumulated 3SP and failed to grow on 3SP. Schürmann et al. 2013 (PMID:23772073) showed that an unmarked $\Delta act$ deletion mutant retained growth on TDP and 3SP (indicating an alternative 3SP-activating enzyme in strain TBEA6), whereas the Tn5::mob insertion exerted a polar effect on the downstream 3SP-CoA desulfinase gene acd (B9U6P5, PMID:24317404).
Removal of spurious GO:0033877 (EC:2.8.3.15): B9U6P4 was automatically annotated with EC:2.8.3.15 (succinyl-CoA:(R)-benzylsuccinate CoA-transferase activity, GO:0033877) in the WGS submission KLN58430.1. PMID:23772073 directly refutes this annotation and establishes Act(TBEA6) as a homodimeric succinyl-CoA:3-sulfinopropionate CoA-transferase (GO:0008410).