Function and Evolution of Two Forms of SecDF Homologs in Streptomyces coelicolor

Abstract

The general secretion (Sec) pathway plays a prominent role in bacterial protein export, and the accessory component SecDF has been shown to improve transportation efficiency. Inspection of Streptomyces coelicolor genome reveals the unexpected presence of two different forms of secDF homologous genes: one in fused form (secDF) and the other in separated form (secD and secF). However, the functional role of two SecDF homologs in S. coelicolor has not yet been determined. Transcriptional analysis of secDF homologs reveals that these genes are constitutively expressed. However, the transcript levels of secD and secF are much higher than that of secDF in S. coelicolor. Deletion of secDF or/and secD/secF in S. coelicolor did result in reduced secretion efficiency of Xylanase A and Amylase C, suggesting that they may have redundant functions for Sec-dependent translocation pathway. Moreover, our results also indicate that SecD/SecF plays a more prominent role than SecDF in protein translocation. Evolutionary analysis suggests that the fused and separated SecDF homologs in Streptomyces may have disparate evolutionary ancestries. SecD/SecF may be originated from vertical transmission of existing components from ancestor of Streptomyces species. However, SecDF may be derived from bacterial ancestors through horizontal gene transfer. Alternately, it is also plausible that SecDF may have arisen through additional gene duplication and fusion events. The acquisition of a second copy may confer a selective benefit to Streptomyces by enhancing protein transport capacity. Taken together, our results provide new insights into the potential biological function and evolutionary aspects of the prokaryotic SecDF complex.

Comprehensive subcellular topologies of polypeptides in Streptomyces

“…Single copies of SecA, SecY, SecE, SecG, that form the core essential Sec translocase [ 16 ], Trigger factor (TF), signal recognition ribonucleoparticle (SRP; Ffh protein component), and the SRP receptor (FtsY protein) were identified. SecD (A0A076M8T9) and SecF (D6EPR3), that are auxiliary components of the translocase, are present both as separate proteins, and in an additional form in which they are fused in a single polypeptide SecDF (D6EKP9), that was previously reported in S. coelicolor [ 44 , 45 ]. Functionally, SecD and SecF, and the fused SecDF may function as membrane-integrated chaperones driving using the proton motive force (PMF) [ 46 ].…”

Genomic data mining reveals a rich repertoire of transport proteins in Streptomyces

“…The fused secDF is present in seven Streptomyces genomes. Unlike most bacteria that have one of the two forms, the majority of Streptomyces species have both the separated form and the fused form [ 37 ]. The acquisition of a second copy may confer a selective advantage to Streptomyces by enhancing the capacity and the effectiveness of protein transport.…”

A Novel Two-Component System, Encoded by the sco5282/sco5283 Genes, Affects Streptomyces coelicolor Morphology in Liquid Culture

“…The Sec system component SecDF ( sco6160 ) was also greatly overexpressed in the dispersed strain. This protein consists of domains paralogous to SecD and SecF, but fused into a single polypeptide, which is normally expressed at very low levels (Zhou et al, 2014). It appears to be part of an operon which includes a two-component system, since all these genes had similar expression levels.…”