Structure of Ca2+-binding protein-6 from Entamoeba histolytica and its involvement in trophozoite proliferation regulation.

Deepshikha Verma,Kandala V R Chary,Aruna Murmu,Samudrala Gourinath,Alok Bhattacharya,William A Petri

doi:10.1371/journal.ppat.1006332

Abstract

Cell cycle of Entamoeba histolytica, the etiological agent of amoebiasis, follows a novel pathway, which includes nuclear division without the nuclear membrane disassembly. We report a nuclear localized Ca2+-binding protein from E. histolytica (abbreviated hereafter as EhCaBP6), which is associated with microtubules. We determined the 3D solution NMR structure of EhCaBP6, and identified one unusual, one canonical and two non-canonical cryptic EF-hand motifs. The cryptic EF-II and EF-IV pair with the Ca2+-binding EF-I and EF-III, respectively, to form a two-domain structure similar to Calmodulin and Centrin proteins. Downregulation of EhCaBP6 affects cell proliferation by causing delays in transition from G1 to S phase, and inhibition of DNA synthesis and cytokinesis. We also demonstrate that EhCaBP6 modulates microtubule dynamics by increasing the rate of tubulin polymerization. Our results, including structural inferences, suggest that EhCaBP6 is an unusual CaBP involved in regulating cell proliferation in E. histolytica similar to nuclear Calmodulin.

Highlights

Ca2+ and Ca2+-binding proteins (CaBPs) such as Calmodulin (CaM), Centrins and Annexins have been implicated in cell cycle regulation and progression in many eukaryotes [1,2]
EhCaBP6, a nucleo-cytosolic Ca2+-binding protein, is a microtubule end binding protein and overexpression of its gene induces an increase in number of microtubular assemblies in E. histolytica
Overall our results show the importance of EhCaBP6 in the regulation of cell proliferation in E. histolytica, a feature not observed in other parasites

Summary

Introduction

Ca2+ and Ca2+-binding proteins (CaBPs) such as Calmodulin (CaM), Centrins and Annexins have been implicated in cell cycle regulation and progression in many eukaryotes [1,2]. The nuclear localized CaM plays the role of a major signal-transducing factor during the cell cycle [2,5]. Centrins are present in the centrioles and they are required for the centriole duplication [9,10] They are considered to play a role in severing of microtubules by causing calcium-mediated contraction. CaBP Annexin II was shown to have an increased expression in HeLa cells at the G1/S and S/G2 boundaries [13]. A significant role of Ca2+ and CaBPs emerges in the regulation of cell cycle progression

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Discussion

Conclusion