Characterization of PAS domains in Frankia and selected Actinobacteria and their possible interaction with other co-domains for environmental adaptation

Abstract : Functional domains are semi-autonomous parts of proteins. The Per-Arnt-Sim (PAS) domain functions as signal-sensor in two-component systems of several bacteria. This domain exhibits large sequence diversity and is linked to other co-domains to modulate their function. In the present study, we analyzed the PAS domains found in the proteomes of several actinobacteria representing a variety of niches. PAS-domain containing proteins were identified with the HMMER program and characterized via an in silico approach. In general, the PAS proteins were found to be in the COG T (signal transduction) category implying their role was indeed in signal transduction. Most of the PAS proteins were found to be structurally conserved and moderately expressed. However, they showed a strong bias towards the lagging strand which may be a result of their involvement in adaptive evolution. A structure based phylogenetic analysis showed that PAS domains with similar interacting co-domains grouped together in a cluster irrespective of the bacterial genus from which they were identified. Thus, we may say that the association of PAS with its co-domains is based upon the PAS domain structure and not on the sequence.