Magnetochrome: a c-type cytochrome domain specific to magnetotatic bacteria. (21st November 2012)

• Record Type: Journal Article
• Authors: Siponen, Marina I.; Adryanczyk, Géraldine; Ginet, Nicolas; Arnoux, Pascal; Pignol, David
• Is Part Of: Biochemical Society transactions. Volume 40:Number 6(2012)
• Page Start: 1319
• Page End: 1323
• Publication Date: 2012-11-21
• Subjects: biomineralization -- c-type cytochrome -- greigite (Fe3S4) -- magnetite (Fe3O4) -- magnetochrome -- magnetotactic bacterium; Biochemistry -- Congresses; 572
• DOI: 10.1042/BST20120104
• Languages: English
• ISSNs: 0300-5127

Abstract

Abstract : Magnetotactic bacteria consist of a group of taxonomically, physiologically and morphologically diverse prokaryotes, with the singular ability to align with geomagnetic field lines, a phenomenon referred to as magnetotaxis. This magnetotactic property is due to the presence of iron-rich crystals embedded in lipidic vesicles forming an organelle called the magnetosome. Magnetosomes are composed of single-magnetic-domain nanocrystals of magnetite (Fe3 O4 ) or greigite (Fe3 S4 ) embedded in biological membranes, thereby forming a prokaryotic organelle. Four specific steps are described in this organelle formation: (i) membrane specialization, (ii) iron acquisition, (iii) magnetite (or greigite) biocrystallization, and (iv) magnetosome alignment. The formation of these magnetic crystals is a genetically controlled process, which is governed by enzyme-catalysed processes. On the basis of protein sequence analysis of genes known to be involved in magnetosome formation in Magnetospirillum magneticum AMB-1, we have identified a subset of three membrane-associated or periplasmic proteins containing a double cytochrome c signature motif CXXCH: MamE, MamP and MamT. The presence of these proteins suggests the existence of an electron-transport chain inside the magnetosome, contributing to the process of biocrystallization. We have performed heterologous expression in E. coli of the cytochrome c motif-containing domains of MamE, MamP and MamT. Initial biophysical characterization has confirmed that MamE, MamP and MamT are indeed c -type cytochromes. Furthermore, determination of redox potentials for this new family of c -type cytochromes reveals midpoint potentials of −76 and −32 mV for MamP and MamE respectively.