Formation of a heterooctameric complex between aspartate α-decarboxylase and its cognate activating factor, PanZ, is CoA-dependent.
Bottom Line: The existence of a fifth essential protein for pantothenate biosynthesis in some enteric bacteria has recently been reported by Stuecker et al.  and Nozaki et al. (in press) .This protein, PanZ, catalyses the activation of the PanD zymogen to form ADC and is essential for prototrophic growth.These approaches reveal that the two proteins interact with nanomolar affinity in a CoA-dependent fashion to form a heterooctameric complex.
Affiliation: School of Chemistry, University of Leeds, Leeds LS2 9JT, UK.Show MeSH
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Mentions: The two series of titration experiments suggest that the two proteins and CoA are in an approximately 1:1:1 ratio. We used electrospray mass spectrometry of the proteins to determine the true stoichiometry of the interaction. We initially examined homomultimerisation of each of the proteins independently. The mass spectrum of PanZ revealed two major species (m/z 15614 and 16381 Da) corresponding to apo PanZ and PanZ bound to CoA: sufficient tertiary structure is retained in the gas-phase to maintain cofactor binding. We also observed an additional minor component at higher MW (m/z 17148 Da), resembling PanZ bound to two equivalents of CoA – we hypothesise that this second species corresponds to PanZ bound to the covalent CoA disulphide. For PanD, a major component (m/z 63.0 kDa) consistent with the tetramer of T57V together with a smaller component (m/z 61.7 kDa) corresponding to a heterotetrameric species in which C-terminal truncation had occurred in one protomer (Fig. 3b). This was confirmed by MS–MS of this species to dissociate the tetramer into full length protomer (m/z 15.753 kDa) and a truncated polypeptide (14.442 kDa).
Affiliation: School of Chemistry, University of Leeds, Leeds LS2 9JT, UK.