ABSTRACT
The nuclear actin-related proteins Arp7 and Arp9 are components of the yeast SWI/SNF and RSC chromatin-remodelling complexes. The 3.1â Å resolution crystal structure reported here shows that the full-length Arp7 and Arp9 proteins exist as a dimer without a requirement for additional polypeptides. Of the 11 actin-related proteins, Arp7 and Arp9 are the only two directly demonstrated to form a dimer within this family. The Arp7-Arp9 heterodimer is unlikely to form an actin-like filament based on modelling using the structure. The Arp7-Arp9 structure reveals that its dimerization interface is not altered when bound in a complex with the SWI/SNF Snf2 HSA domain and the regulatory protein Rtt102.
Subject(s)
Carrier Proteins/chemistry , Chromosomal Proteins, Non-Histone/chemistry , Saccharomyces cerevisiae Proteins/chemistry , Saccharomyces cerevisiae/chemistry , Transcription Factors/chemistry , Amino Acid Sequence , Carrier Proteins/genetics , Chromosomal Proteins, Non-Histone/genetics , Crystallography, X-Ray , Escherichia coli/genetics , Escherichia coli/metabolism , Models, Molecular , Molecular Sequence Data , Protein Binding , Protein Multimerization , Protein Structure, Secondary , Protein Structure, Tertiary , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Saccharomyces cerevisiae/genetics , Saccharomyces cerevisiae Proteins/genetics , Transcription Factors/geneticsSubject(s)
Carrier Proteins , Point Mutation/physiology , Retinal Dystrophies/metabolism , Retinal Pigment Epithelium/metabolism , Vision, Ocular/physiology , Alcohol Oxidoreductases/metabolism , Carrier Proteins/chemistry , Carrier Proteins/genetics , Carrier Proteins/metabolism , Crystallography, X-Ray , Humans , Oxidation-Reduction , Protein Structure, Secondary , Protein Structure, Tertiary , Retinal Dystrophies/classification , Retinal Dystrophies/genetics , Retinaldehyde/metabolismABSTRACT
Cellular retinaldehyde-binding protein (CRALBP) is essential for mammalian vision by routing 11-cis-retinoids for the conversion of photobleached opsin molecules into photosensitive visual pigments. The arginine-to-tryptophan missense mutation in position 234 (R234W) in the human gene RLBP1 encoding CRALBP compromises visual pigment regeneration and is associated with Bothnia dystrophy. Here we report the crystal structures of both wild-type human CRALBP and of its mutant R234W as binary complexes complemented with the endogenous ligand 11-cis-retinal, at 3.0 and 1.7 A resolution, respectively. Our structural model of wild-type CRALBP locates R234 to a positively charged cleft at a distance of 15 A from the hydrophobic core sequestering 11-cis-retinal. The R234W structural model reveals burial of W234 and loss of dianion-binding interactions within the cleft with physiological implications for membrane docking. The burial of W234 is accompanied by a cascade of side-chain flips that effect the intrusion of the side-chain of I238 into the ligand-binding cavity. As consequence of the intrusion, R234W displays 5-fold increased resistance to light-induced photoisomerization relative to wild-type CRALBP, indicating tighter binding to 11-cis-retinal. Overall, our results reveal an unanticipated domino-like structural transition causing Bothnia-type retinal dystrophy by the impaired release of 11-cis-retinal from R234W.
