Josh MacCready

  • Jan 23, 2018

Date & Location: January 23, 2018 , at 12p; Room 168 Plant Biology Building

Subject: Protein gradients on the nucleoid position the carbon-fixing organelles of cyanobacteria

Abstract: Carboxysomes are protein-based bacterial organelles that encapsulate key enzymes of the Calvin-Benson-Bassham cycle. Previous work has implicated a ParA-like protein (hereafter McdA) as important for spatial position of carboxysomes along the longnitudal axis of the model cyanobacterium Synechococcus elongatus PCC 7942.

Yet, how self-organization of McdA emerges and contributes to carboxysome position is unknown. Here, we show that a small protein, termed McdB, localizes to carboxysomes through an interaction with the shell proteins CcmK2, CcmK3 and CcmK4 to drive emergent oscillatory patterning of McdA on the nucleoid. Our results demonstrate that carboxysome-dependent McdA depletion zone formation on the nucleoid is required for directed motion of carboxysomes towards increased concentrations of McdA. We propose that McdA/McdB are a new class of self-organizing proteins that follow a Brownian-ratchet mechanism for equidistant positioning of carboxysomes in cyanobacteria and have broader implications for understanding the spatial positioning of protein mega-complexes and organelles in other bacteria.

Josh MacCready is a graduate student in the lab of Danny Ducat.