Towards a quantitative assessment of the integral magnetosome membrane sub-proteome

ABSTRACT: Magnetosomes are membranous organelles than contain crystals of magnetic minerals and enable magnetotactic bacteria to orientate in magnetic fields. The enveloping magnetosome membrane was found to contain a subset of specific proteins that are encoded within a genomic island. However, along with proteins that are bona fide and confirmed magnetosome proteins, proteomic studies repetitively revealed the presence of numerous other and partially highly abundant proteins within the magnetosome membrane fraction, which could not yet clearly be discriminated as contaminants, acquired during purification from other cellular compartments, or as genuine integral magnetosome membrane proteins. In order to clearly identify all proteins from the magnetotactic Alphaproteobacterium Magnetospirillum gryphiswaldense that are specifically targeted to the magnetosome membrane and to estimate their abundancy, we analyzed the protein composition of several cellular fractions by semi-quantitative mass spectrometry. Although spectra from over 1000 proteins were found within the magnetosome membrane fraction, our comparative approach could exclude most of them as contaminants. We found that almost all specifically magnetosome membrane-integral proteins belong to a well-defined subgroup of previously identified magnetosome-associated proteins, indicating that the protein composition of the compartment is strongly controlled. Furthermore, the correlation of our semi-quantitative proteome data with recently published quantitative Western blot and cryo-electron tomography results revealed that the magnetosome membrane is tightly packed with transmembrane domains of integral proteins, indicating a very high protein composition of the membrane. Our findings will help to further define the structure of the organelle and contribute to the elucidation of the processes involved in biogenesis of magnetosomes.

INSTRUMENT(S):

ORGANISM(S): Magnetospirillum Gryphiswaldense

SUBMITTER: Andreas Otto  

LAB HEAD: Dr. Andreas Otto

PROVIDER: PXD006166 | Pride | 2017-10-24

REPOSITORIES: Pride