The Atypical Hybrid Histidine Protein Kinase RodK in Myxococcus xanthus : Spatial Proximity Supersedes Kinetic Preference in Phosphotransfer Reactions

Abstract

Many proteins of two-component signal transduction systems (TCS) have domain structures that do not comply with a phosphate flow as observed in linear TCS, phosphorelays, or simple branched pathways. An example is RodK, which is essential for fruiting body formation in Myxococcus xanthus and, in addition to a sensor domain, consists of a kinase domain and three receiver domains (RodK-R1, -R2, and -R3), all of which are functionally important. We identified the RokA response regulator as part of the RodK pathway. In vitro the isolated RodK kinase domain engages in phosphotransfer to RodK-R3 and RokA, with a kinetic preference for RokA. However, in the context of the full-length protein, the RodK kinase domain has a preference for phosphotransfer to RodK-R3 over RokA. We suggest that in full-length RodK, the spatial proximity of the RodK kinase domain and RodK-R3 compensate for the kinetic preference of the isolated kinase domain for RokA. Thus, the kinetic preference observed using an isolated kinase domain of a hybrid kinase does not necessarily reflect the phosphotransfer preference of the full-length protein. We speculate that the phosphorylation status of RodK-R1 and RodK-R2 determines whether RodK engages in phosphotransfer to RodK-R3 or RokA in vivo.

The orphan histidine protein kinase SgmT is a c‐di‐GMP receptor and regulates composition of the extracellular matrix together with the orphan DNA binding response regulator DigR in Myxococcus xanthus

“…S2B). In the case of hybrid kinases, an in vitro kinetic preference for a separate response regulator over its own receiver domain using isolated domains can be outperformed in the context of the full‐length kinase protein by the spatial proximity of the in cis receiver (Wegener‐Feldbrügge and Søgaard‐Andersen, 2009). However, this does not seem to be the case for SgmT because phosphotransfer to DigR was also observed with a SgmT variant consisting of the kinase and receiver domains as well with full‐length SgmT.…”

Cross Talk Inhibition Nullified by a Receiver Domain Missense Substitution

“…If ArcB and BarA are direct phosphoryl donors to the NarL V88A protein, one would presume that cross talk involves phosphoryl transfer from the ArcB and BarA Hpt domains (83). However, DHp domains in hybrid sensors have relaxed interaction specificities for their intramolecular receiver domain (84)(85)(86), so perhaps the NarL V88A substitution unmasks phosphoryl transfer directly from the ArcB and BarA transmitter domains. In this context, it is intriguing that computational analyses have identified NarP as among the top-scoring potential partners for interaction with the DHp domains of ArcB and BarA, among others (84).…”

Intra- and Interprotein Phosphorylation between Two-hybrid Histidine Kinases Controls Myxococcus xanthus Developmental Progression

“…HyHPKs can also function in the absence of histidine phosphotransferase proteins. In these cases, the fused REC domain(s) have been shown to modulate signal transmission to a cognate RR by functioning to inactivate the associated kinase (13) and/or to provide sites for alternative kinase phosphorylation presumably leading to signal integration (14). Thus, HyHPKs provide an excellent example of how the highly modular nature of His-Asp phosphorelays can be exploited to generate complex signaling systems.…”