The Acidic Repetitive Domain of the Magnetospirillum gryphiswaldense MamJ Protein Displays Hypervariability but Is Not Required for Magnetosome Chain Assembly

Abstract

Magnetotactic bacteria navigate along the earth's magnetic field using chains of magnetosomes, which are intracellular organelles comprising membrane-enclosed magnetite crystals. The assembly of highly ordered magnetosome chains is under genetic control and involves several specific proteins. Based on genetic and cryo-electron tomography studies, a model was recently proposed in which the acidic MamJ magnetosome protein attaches magnetosome vesicles to the actin-like cytoskeletal filament formed by MamK, thereby preventing magnetosome chains from collapsing. However, the exact functions as well as the mode of interaction between MamK and MamJ are unknown. Here, we demonstrate that several functional MamJ variants from Magnetospirillum gryphiswaldense and other magnetotactic bacteria share an acidic and repetitive central domain, which displays an unusual intra-and interspecies sequence polymorphism, probably caused by homologous recombination between identical copies of Glu-and Pro-rich repeats. Surprisingly, mamJ mutant alleles in which the central domain was deleted retained their potential to restore chain formation in a ⌬mamJ mutant, suggesting that the acidic domain is not essential for MamJ's function. Results of two-hybrid experiments indicate that MamJ physically interacts with MamK, and two distinct sequence regions within MamJ were shown to be involved in binding to MamK. Mutant variants of MamJ lacking either of the binding domains were unable to functionally complement the ⌬mamJ mutant. In addition, two-hybrid experiments suggest both MamK-binding domains of MamJ confer oligomerization of MamJ. In summary, our data reveal domains required for the functions of the MamJ protein in chain assembly and maintenance and provide the first experimental indications for a direct interaction between MamJ and the cytoskeletal filament protein MamK.

Genomic insights into the uncultured genus ‘Candidatus Magnetobacterium’ in the phylum Nitrospirae

“…MamK protein assembles into actinlike filaments that are involved in the formation of magnetosome chains in Proteobacteria MTB (Komeili et al, 2006;Katzmann et al, 2010;Draper et al, 2011;Ozyamak et al, 2013). An acidic protein, MamJ, interacts with MamK and has important role in chain forming and dynamic turnover of MamK filaments (Scheffel et al, 2006;Scheffel and Schü ler, 2007;Draper et al, 2011). Intriguingly, Mcas has only one copy of mamK and no mamJ despite that the numerous magnetosome chains assembled inside cells (Figure 4).…”

Formation of magnetite by bacteria and its application

“…MamJ is an acidic protein associated with the filamentous structure, and it directs the assembly of the BacMP chain (Scheffel et al 2006). Direct interaction between MamJ and MamK has been revealed, and it is proposed that MamJ plays a role in chain assembly and maintenance (Scheffel & Schuler 2007).…”

Magnetita biomimética mediada por proteínas del magnetosoma vs. magnetita del meteorito ALH84001: ¿Son ambas comparables?

“…However, MamK is not only a merely rigid backbone, but also has an active function in positioning and concatenating magnetosome chains (Katzmann et al, 2010). MamJ physically interacts with MamK, with two distinct sequence regions involved in binding to MamK, and that direct interaction allow the formation of the magnetosome chain (Scheffel and Schüler, 2007). Interstingly, mamJ and mamK genes are cotranscribed (Scheffel et al, 2006), strengthen the interpretation that both complement each other as two of the main responsible of the arrangement of magnetosomes into chains.…”

“…MamG, MamF, MamD and MamC are all encoded in the mamGFDC operon. It has been observed that the deletion of the entire mamGFDC operon does not abolish the formation of magnetite crystals, but cells produce crystals that are only 75% of the wild-type size and are less regular than wild-type (Scheffel et al, 2007). These authors also suggested that the MamGFDC proteins have partially redundant functions and control the growth of magnetite crystals in a cumulative manner.…”

“…Unfortunately, only three of these proteins have been studied so far in in vitro experiments. Although some other proteins and operons have been studied in mutants lacking the specific gene (or genes) of interest (Scheffel et al, 2007;Ding et al, 2010;Murat et al, 2010;Murat et al, 2012;Tanaka et al, 2011;Arakaki et al, 2014), the results are not yet conclusive, because there are many other factors that may influence those results. MamC (Valverde-Tercedor et al, 2015), Mms6 (Ameniya et al, 2007;Prozorov et al, 2007;Arakaki et al, 2010;Rawlings et al, 2016) and MmsF (Rawlings et al, 2014) have been expressed as recombi-…”