title: The regulatory factor SipA is a highly stable beta-II class protein with a SH3 fold.
abstract: The small regulator SipA, interacts with the ATP-binding domain of non-bleaching sensor histidine kinase (NblS), the most conserved histidine kinase in cyanobacteria. NblS regulates photosynthesis and acclimation to a variety of environmental conditions. We show here that SipA is a highly stable protein in a wide pH range, with a thermal denaturation midpoint of 345 K. Circular dichroism and 1D 1H NMR spectroscopies, as well as modelling, suggest that SipA is a beta-II class protein, with short strands followed by turns and long random-coil polypeptide patches, matching the SH3 fold. The experimentally determined m-value and the heat capacity change upon thermal unfolding (DeltaCp) closely agreed with the corresponding theoretical values predicted from the structural model, further supporting its accuracy.
authors.affiliation: Macromolecular Crystallography Unit, Instituto de Biomedicina de Valencia (CSIC) and CIBERER, 46010 Valencia, Spain.
authors.forename: María Luisa
authors.initials: ML
authors.lastname: López-Redondo
authors.forename: Asunción
authors.initials: A
authors.lastname: Contreras
authors.forename: Alberto
authors.initials: A
authors.lastname: Marina
authors.forename: José L
authors.initials: JL
authors.lastname: Neira
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D002942:Circular Dichroism; D009682:Magnetic Resonance Spectroscopy; D017510:Protein Folding; D055550:Protein Stability; D013816:Thermodynamics; D018909:src Homology Domains / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins