The mechanics of translocation

jerry submitted, created time 7 months 6 days (www.sciencedirect.com)

Stepwise addition of amino acids to the growing polypeptide chain requires the coordinated movement of mRNA and tRNAs through the ribosome, a process known as translocation. Researchers review current understanding of the kinetics and mechanics of translocation, with emphasis on the structure of a functional mammalian ribosome stalled during translocation by an mRNA pseudoknot.

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Too long for translocation?

sea-maid submitted, created time 7 months 4 weeks (www.jcb.org)

To explore SRP's role in vivo, the authors of this paper prepared a mutated version of human SRP14 that specifically lacked the delaying function.

SRP14's ability to bind to nascent peptides and to the SRP receptor remained intact. In cells that carried the mutant SRP, elongation sped up, but the final concentration of secreted protein dropped and growth suffered. Closer inspection revealed that translocation in these cells had slowed down and nascent peptide chains were being degraded.

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Contribution of hydrophobic and electrostatic interactions to the membrane integration of the Shaker K+ channel voltage sensor domain

penguin submitted, created time 1 year 7 months (www.pnas.org)

"Membrane-embedded voltage-sensor domains in voltage-dependent potassium channels (Kv channels) contain an impressive number of charged residues. How can such highly charged protein domains be efficiently inserted into biological membranes? In the plant Kv channel KAT1, the S2, S3, and S4 transmembrane helices insert cooperatively, because the S3, S4, and S3-S4 segments do not have any membrane insertion ability by themselves

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Dynamics of the unbound head during myosin V processive translocation

nomad submitted, created time 1 year 10 months (www.nature.com)

Myosin V moves cargoes along actin filaments by walking hand over hand. Although numerous studies support the basic hand-over-hand model, little is known about the fleeting intermediate that occurs when the rear head detaches from the filament. Here we use submillisecond dark-field imaging of gold nanoparticle–labeled myosin V to directly observe the free head as it releases from the actin filament, diffuses forward and rebinds. We find that the unbound head rotates freely about the lever-arm junction, a trait that likely facilitates travel through crowded actin meshworks.

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