In silico Structural and Functional Analysis of Arabidopsis thaliana's XPB Homologs

Arabidopsis thaliana has two homologs of the corresponding human xeroderma pigmentosum group B (XPB) helicase protein. The proteins namely AtXPB1 and AtXPB2, which are 95% similar, participate in transcription and Nucleotide Excision Repair. We used bioinformatic tools to investigate the phylogeny, structure, domains, docking site, and interactome of the two paralogs in order to reveal their functional differences. This study suggests that AtXPB1 interacts with Farnesyl Pyrophosphate Synthase 2 (FPS2), a rate-limiting enzyme in the synthesis of brassinosteroids, and Heat Shock Protein 90 (AtHSP90), such interactions were absent from the AtXPB2 interactome. AtXPB1 may be required to regulate the activity of Farnesyl Pyrophosphate Synthase 2, which controls the levels of brassinosteroids, phytohormones that control multiple physiological processes required for normal plant growth and development. In addition, AtXPB1 may have better oxidative stress tolerance than AtXPB2 as AtHSP90 seems to stabilize and protect the former from the proteasomal degradation induced by oxidative stress. These results were applied to the previously observed phenotypic characteristics of atxpb1(-/-) mutants which show great sensitivity to the oxidative stress-inducing agent hypochlorous acid, and experience absence of germination synchrony, lower seed germination rate, and delay in organ differentiation