Abstract
Chemosensory pathways correspond to major signal transduction mechanisms and can be classified into the functional families flagellum-mediated taxis, type four pili-mediated taxis or pathways with alternative cellular functions (ACF). CheR methyltransferases are core enzymes in all of these families. CheR proteins fused to tetratricopeptide repeat (TPR) domains have been reported and we present an analysis of this uncharacterized family. We show that CheR-TPRs are widely distributed in GRAM-negative but almost absent from GRAM-positive bacteria. Most strains contain a single CheR-TPR and its abundance does not correlate with the number of chemoreceptors. The TPR domain fused to CheR is comparatively short and frequently composed of 2 repeats. The majority of CheR-TPR genes were found in gene clusters that harbor multidomain response regulators in which the REC domain is fused to different output domains like HK, GGDEF, EAL, HPT, AAA, PAS, GAF, additional REC, HTH, phosphatase or combinations thereof. The response regulator architectures coincide with those reported for the ACF family of pathways. Since the presence of multidomain response regulators is a distinctive feature of this pathway family, we conclude that CheR-TPR proteins form part of ACF type pathways. The diversity of response regulator output domains suggests that the ACF pathways form a superfamily which regroups many different regulatory mechanisms, in which all CheR-TPR proteins appear to participate. In the second part we characterize WspC of Pseudomonas putida, a representative example of CheR-TPR. The affinities of WspC-Pp for S-adenosylmethionine and S-adenosylhomocysteine were comparable to those of prototypal CheR, indicating that WspC-Pp activity is in analogy to prototypal CheRs controlled by product feed-back inhibition. The removal of the TPR domain did not impact significantly on the binding constants and consequently not on the product feed-back inhibition. WspC-Pp was found to be monomeric, which rules out a role of the TPR domain in self-association.
Highlights
In the second part we report the analysis of a representative example of a CheR-tetratricopeptide repeat (TPR) protein as well as truncated versions thereof lacking the TPR domain
The final list contained 132 CheR-TPR proteins that were encoded in 96 genomes
CheR-TPR proteins are very rare in Gammaproteobacteria and Firmicutes
Summary
In many cases single-domain proteins have evolved with the capacity to recognize other proteins or to oligomerize. An alternative evolutionary strategy consists in fusion proteins in which one domain is dedicated to binding other proteins. An example for such domains is the tetratricopeptide repeat (TPR) containing domain [1]. A. TPR is composed of 34 amino acids which form a pair of antiparallel helices connected by a short loop [2]. A TPR domain possess multiple, repetitive TPRs. The TPR was discovered as late as in 1990 [3] and since the number of reports on different types of TPR domain containing proteins keeps growing
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