Discovery of bacteriorhodopsins in Haloarchaeal species isolated from Indian solar salterns: deciphering the role of the N-terminal residues in protein folding and functional expression.

Dipesh Kumar Verma,Ishita Baral,Senthil E Prasad,Atul Kumar,Krishan Gopal Thakur

doi:10.1111/1751-7915.13359

Abstract

SummaryInteresting optical and photochemical properties make microbial rhodopsin a promising biological material suitable for various applications, but the cost‐prohibitive nature of production has limited its commercialization. The aim of this study was to explore the natural biodiversity of Indian solar salterns to isolate natural bacteriorhodopsin (BR) variants that can be functionally expressed in Escherichia coli. In this study, we report the isolation, functional expression and purification of BRs from three pigmented haloarchaea, wsp3 (water sample Pondicherry), wsp5 and K1T isolated from two Indian solar salterns. The results of the 16S rRNA data analysis suggest that wsp3, wsp5 and K1T are novel strains belonging to the genera Halogeometricum, Haloferax and Haloarcula respectively. Overall, the results of our study suggest that 17 N‐terminal residues, that were not included in the gene annotation of the close sequence homologues, are essential for functional expression of BRs. The primary sequence, secondary structural content, thermal stability and absorbance spectral properties of these recombinant BRs are similar to those of the previously reported Haloarcula marismortui HmBRI. This study demonstrates the cost‐effective, functional expression of BRs isolated from haloarchaeal species using E. coli as an expression host and paves the way for feasibility studies for future applications.

Highlights

Due to the constant depletion of existing fossil fuel reserves and global climate change, there is an urgent need to exploit alternate renewable energy sources to meet ever-increasing energy demands
BR was first isolated from a strain of Halobacterium halobium and has been extensively studied (Oesterhelt and Stoeckenius, 1971; Lozier et al, 1975)
The successful expression of the recombinant BRs using E. coli reported in this study provides a basis for exploiting these proteins for industrial/commercial applications and for correcting annotation errors in submitted genomes

Summary

Introduction

Due to the constant depletion of existing fossil fuel reserves and global climate change, there is an urgent need to exploit alternate renewable energy sources to meet ever-increasing energy demands. BR can remain in the Q state for 7 to 12 years and returns to its normal bR state upon red photon illumination (Stuart et al, 1996, 2002) These unique features coupled with high stability make BR a versatile biological material with numerous potential attractive applications in photovoltaic cells (Hong, 1994; Xu et al, 2003; Chellamuthu et al, 2016), artificial retina (Chen and Birge, 1993; Cutsuridis and Wennekers, 2009), biosensors (Boucher et al, 1996; Lanyi and Luecke, 2001), optical memory storage devices (Birge et al, 1990, 1999; Stuart et al, 1996, 2002) and optogenetics (Lindvold and Lausen, 2006; Fabian et al, 2011).

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Conclusion