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The first structure of a ribozyme that catalyzes the stereospecific carbon-carbon bond formation between two small molecules shows how an RNA active site can perform the synthetically important Diels-Alder reaction. Surprisingly, the ribozyme active site shares structural features with proteins that catalyze the same reaction.
Glutamate receptor ion channels are multidomain membrane proteins that mediate excitatory synaptic responses in the brain and spinal cord. Single-particle electron microscopy reveals their molecular envelope and how this changes during desensitization.
Two recent papers characterize a protein complex that is part of the budding yeast kinetochore, the specialization that links chromosomal DNA with one or more spindle microtubules. Both studies present convincing evidence that this complex can assemble into rings or helices that wrap around microtubules.
Gating of the mechanosensitive channel MscS involves cooperative action of glycine and alanine residues along the pore-lining transmembrane helix. Opening of the channel is facilitated by an iris-like rotation and tilt of the pore-lining helices. Site-directed mutagenesis indicates that substantial structural plasticity can be tolerated by MscS without impairing its function.
A FRET-based approach to monitor the assembly of membrane-associated COPII coat proteins provides new insights into how the COPII–cargo complex is maintained on the membrane during continuous rounds of Sar1p-GTP hydrolysis.
A recent study shows that the testicular angiotensin converting enzyme (ACE) has a new unexpected activity: it is responsible for cleaving GPI off from proteins anchored on the sperm cell membrane.
Despite its simple repeating sequence, the C-terminal domain (CTD) of RNA polymerase II spatially and temporally recruits diverse factors to the site of transcription. A recent study reports observations consistent with an induced fit binding mechanism that is coupled to recognition of CTD proline isomerization and phosphorylation patterns.
The deletion of residue 508 in CFTR is the most common cystic fibrosis–causing mutation. Recent studies indicate that the main chain and side chain of this residue contribute to the proper folding of CFTR at different stages.
New work places the Hsp70/DnaK system in an opening role in protein disaggregation, facilitating the extraction of individual polypeptides from the aggregate surface to the axial channel of Hsp104/ClpB. It also reinforces a long-standing belief that reactivation rather than simple clearance of aggregated protein is necessary for cell stress tolerance.
In mammals, a soluble bicarbonate-regulated adenylyl cyclase is required for sperm fertility. Crystal structures of a cyanobacterial cousin provide new insights into the molecular mechanisms of activation and catalysis in soluble adenylyl cyclase and other class III nucleotidyl cyclases.
