The presumptive magnetosome protein Mms16 is a poly(3-hydroxybutyrate) granule-bound protein (phasin) in Magnetospirillum gryphiswaldense

Daniel Schultheiss, René Handrick, Dieter Jendrossek, Marianne Hanzlik, Dirk Schüler
Journal of Bacteriology 2005, 187 (7): 2416-25
The Mms16 protein has been previously found to be associated with isolated magnetosomes from two Magnetospirillum strains. A function of this protein as a magnetosome-specific GTPase involved in the formation of intracellular magnetosome membrane vesicles was suggested. Here we present a study of the Mms16 protein from Magnetospirillum gryphiswaldense to clarify its function. Insertion-duplication mutagenesis of the mms16 gene did not affect the formation of magnetosome particles but resulted in the loss of the ability of M. gryphiswaldense cell extracts to activate poly(3-hydroxybutyrate) (PHB) depolymerization in vitro, which was coincident with loss of the most abundant 16-kDa polypeptide from preparations of PHB granule-bound proteins. The mms16 mutation could be functionally complemented by enhanced yellow fluorescent protein (EYFP) fused to ApdA, which is a PHB granule-bound protein (phasin) in Rhodospirillum rubrum sharing 55% identity to Mms16. Fusions of Mms16 and ApdA to enhanced green fluorescent protein (EGFP) or EYFP were colocalized in vivo with the PHB granules but not with the magnetosome particles after conjugative transfer to M. gryphiswaldense. Although the Mms16-EGFP fusion protein became detectable by Western analysis in all cell fractions upon cell disruption, it was predominantly associated with isolated PHB granules. Contrary to previous suggestions, our results argue against an essential role of Mms16 in magnetosome formation, and the previously observed magnetosome localization is likely an artifact due to unspecific adsorption during preparation. Instead, we conclude that Mms16 in vivo is a PHB granule-bound protein (phasin) and acts in vitro as an activator of PHB hydrolysis by R. rubrum PHB depolymerase PhaZ1. Accordingly, we suggest renaming the Mms16 protein of Magnetospirillum species to ApdA, as in R. rubrum.

Full Text Links

Find Full Text Links for this Article


You are not logged in. Sign Up or Log In to join the discussion.

Related Papers

Remove bar
Read by QxMD icon Read

Save your favorite articles in one place with a free QxMD account.


Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"