Crystal Structure of a Dimeric Chymotrypsin Inhibitor 2 Mutant Containing an Inserted Glutamine Repeat

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 96; no. 4; pp. 1257 - 1261
• Main Authors: Chen, Yu Wai, Stott, Kelvin, Perutz, Max F.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 16.02.1999; National Acad Sciences; National Academy of Sciences; The National Academy of Sciences
• Subjects: Amino Acid Sequence; Atoms; Biochemistry; Biological Sciences; Crystal structure; Crystallography, X-Ray; Crystals; Dimerization; Dimers; Escherichia coli; Glutamine; Huntington disease; Models, Molecular; Molecular Sequence Data; Molecules; Monomers; Mutagenesis, Insertional; Mutation; Neurodegenerative diseases; Peptides - chemistry; Plant Proteins; Protein Conformation; Protein Folding; Proteins; Recombinant Proteins - chemistry; Repetitive Sequences, Amino Acid; Serine Proteinase Inhibitors - chemistry
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.96.4.1257

We have constructed mutants of chymotrypsin inhibitor 2 with short glutamine repeats inserted into its inhibitory loop. These mutants oligomerize when expressed in Escherichia coli. The dimer of a mutant with four glutamines now has been crystallized, and its structure has been solved by molecular replacement by using the wild-type monomer as a search model. The structure of each half of the dimer is found to be the same as that of the wild-type monomer, except around the glutamine insertion. It was proposed that the components of the oligomers are held together by hydrogen bonds between the main-chain and side-chain amides of the glutamine repeats. Instead, they appear to form by swapping domains on folding in E. coli, and the glutamine repeats connecting the components of the dimers are disordered.