Bacterial Magnetosome Biomineralization - A Novel Platform to Study Molecular Mechanisms of Human CDF-Related Type-II Diabetes

Abstract

Cation diffusion facilitators (CDF) are part of a highly conserved protein family that maintains cellular divalent cation homeostasis in all organisms. CDFs were found to be involved in numerous human health conditions, such as Type-II diabetes and neurodegenerative diseases. In this work, we established the magnetite biomineralizing alphaproteobacterium Magnetospirillum gryphiswaldense as an effective model system to study CDF-related Type-II diabetes. Here, we introduced two ZnT-8 Type-II diabetes-related mutations into the M. gryphiswaldense MamM protein, a magnetosome-associated CDF transporter essential for magnetite biomineralization within magnetosome vesicles. The mutations' effects on magnetite biomineralization and iron transport within magnetosome vesicles were tested in vivo. Additionally, by combining several in vitro and in silico methodologies we provide new mechanistic insights for ZnT-8 polymorphism at position 325, located at a crucial dimerization site important for CDF regulation and activation. Overall, by following differentiated, easily measurable, magnetism-related phenotypes we can utilize magnetotactic bacteria for future research of CDF-related human diseases.

The dual role of MamB in magnetosome membrane assembly and magnetite biomineralization

“…S4A). Comparing the degree‐of‐openness values between the two MamB QH‐2 structures to those in other CTD‐CDF structures indicated that the two MamB QH‐2 CTDs showed closer similarity to the closed, metal‐bound structures of YiiP (∼30°) (Lu and Fu, ) than to the open, metal‐free structures of CzrB (∼53°) (Cherezov et al ., ) and MamM‐CTD (∼43°) (Zeytuni et al ., ) (Fig. B and C and Supporting Information Fig.…”

Cation Diffusion Facilitator family: Structure and function

“…In addition, it has been suggested that bacterial CDFs may be capable of other activity such as mediating antibiotic resistance as is the case of CepA of Klebsiella pneumoniae that has been linked to chlorhexidine resistance [23], while two CDFs, MamB and MamM from Magnetospirillum gryphiswaldense were recently shown to be involved in magnetosome formation [101]. Interestingly, MamM has been used as a platform for studying CDF‐related type II diabetes because of the ease of measurement of its magnetism‐related phenotypes [114].…”

The cation diffusion facilitator protein MamM’s cytoplasmic domain exhibits metal-type dependent binding modes and discriminates against Mn2+

“…Additionally, three MamM CTD metal binding sites were proposed that included two symmetrical, allosteric peripheral sites (PSs, composed of H264 from one monomer and E289 from the second monomer) and one central site (CS, composed of D249 and H285 from both monomers). Biophysical evidence revealed that zinc binding to the PSs leads to a change in protein conformation from an open, dynamic V-shaped dimer to a much tighter, rigid dimeric packing Barber-Zucker et al, 2019;Zeytuni et al, 2014bZeytuni et al, , 2014a.…”