Translocation intermediate in cellulose synthesis and transport
Jochen Zimmer group (University of Virginia)
The group of Jochen Zimmer at the University of Virginia
determined the structure of a translocation intermediate of a membrane
protein involved in cellulose synthesis and transport. Cellulose, the most
abundant biological macromolecule on the planet, is an extracellular, linear
polymer of glucose molecules. It represents an essential component of plant
cell walls but is also found in algae and bacteria. In bacteria, cellulose
production frequently correlates with the formation of biofilms, a sessile,
multicellular growth form. Cellulose synthesis and transport across the
inner bacterial membrane is mediated by a complex of the multi-spanning
catalytic BcsA subunit and the membrane-anchored, periplasmic BcsB protein.
The authors determined the crystal structure of a remarkable complex of BcsA
and BcsB from Rhodobacter sphaeroides containing a translocating
polysaccharide. The structure of the BcsA-B translocation intermediate
reveals the architecture of the cellulose synthase, demonstrates how BcsA
forms a cellulose-conducting channel, and suggests a model for the coupling
of cellulose synthesis and translocation in which the nascent polysaccharide
is extended by one glucose molecule at a time.
Figure: Orthogonal views of BcsA-B
translocation intermediate, showing a translocating polysaccharide.
Citation: Morgan JLW, Strumillo J, Zimmer J.
Crystallographic snapshot of cellulose synthesis and membrane translocation.
Nature. 2013 January 10; 493: 181-186. doi:10.1038/nature11744