In-silico analysis suggests alterations in the function of XisA protein as a possible mechanism of butachlor toxicity in the nitrogen fixing cyanobacterium Anabaena sp. PCC 7120.

Shilpi Singh,Prem Pal Singh

doi:10.6026/97320630009701

Abstract

Butachlor, a commonly used herbicide adversely affects the nitrogen fixing capability of Anabaena, an acclaimed nitrogen fixer in the Indian paddy fields. The nitrogen fixation in Anabaena is triggered by the excision of nifD element by xisA gene leading to rearrangement of nifD forming nifHDK operon in the heterocyst of Anabaena sp. PCC7120. Functional elucidation adjudged through in-silico analysis revealed that xisA belongs to integrase family of tyrosine recombinase. The predicted functional partners with XisA protein that have shown cooccurence with this protein in a network are mainly hypothetical proteins with unknown functions except psaK1 whose exact function in photosystem I is not yet known. The focus of this study was to find out the relation between XisA and butachlor using in-silico approaches. The XisA protein was modeled and its active sites were identified. Docking studies revealed that butachlor binds at the active site of XisA protein hampering its excision ability vis-à-vis nif genes in Anabaena sp. PCC7120. This study reveals that butachlor is not directly involved in hampering the nitrogen fixing ability of Anabaena sp. PCC7120 but by arresting the excision ability of XisA protein necessary for the functioning of nif gene and nitrogen fixation.

Highlights

Butachlor a commonly used herbicide is frequently used in the rice paddy fields to block the growth of undesirable weeds
The ligand butachlor and the Conclusion: Using in-silico approaches, an attempt has been made for the first time to elucidate that binding of butachlor at the active site of XisA protein hampers the nitrogen fixing mechanism of Anabaena sp
Through docking studies it was revealed that butachor binds at site 3 of the modelled XisA protein and MET231 was present solely at the ligand binding site

Summary

Introduction

Butachlor a commonly used herbicide is frequently used in the rice paddy fields to block the growth of undesirable weeds. PCC7120 is a completely sequenced [1] heterocystous,gram-negative photoautotroph, endowed with two agriculturally important traits of carbon and atmospheric nitrogen fixation within the heterocyst cells It contributes to the global nitrogen economy of soil and supports rice paddy production in tropical countries including. It is known that the nitrogen fixing genes (nif) are wide spread in the genome of Anabaena which harbours an 11,278 kb nifD element, a 59,428 kb fdxN element and a 9419kb hupL element [2]. All these three elements are excised by site-specific recombination process during the late stages of heterocyst differentiation [3, 4]. The loss of excision may ISSN 0973-2063 (online) 0973-8894 (print)

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Discussion

Conclusion