title: A charged residue at the subunit interface of PCNA promotes trimer formation by destabilizing alternate subunit interactions.
abstract: Eukaryotic proliferating cell nuclear antigen (PCNA) is an essential replication accessory factor that interacts with a variety of proteins involved in DNA replication and repair. Each monomer of PCNA has an N-terminal domain A and a C-terminal domain B. In the structure of the wild-type PCNA protein, domain A of one monomer interacts with domain B of a neighboring monomer to form a ring-shaped trimer. Glu113 is a conserved residue at the subunit interface in domain A. Two distinct X-ray crystal structures have been determined of a mutant form of PCNA with a substitution at this position (E113G) that has previously been studied because of its effect on translesion synthesis. The first structure was the expected ring-shaped trimer. The second structure was an unanticipated nontrimeric form of the protein. In this nontrimeric form, domain A of one PCNA monomer interacts with domain A of a neighboring monomer, while domain B of this monomer interacts with domain B of a different neighboring monomer. The B-B interface is stabilized by an antiparallel beta-sheet and appears to be structurally similar to the A-B interface observed in the trimeric form of PCNA. The A-A interface, in contrast, is primarily stabilized by hydrophobic interactions. Because the E113G substitution is located on this hydrophobic surface, the A-A interface should be less favorable in the case of the wild-type protein. This suggests that the side chain of Glu113 promotes trimer formation by destabilizing these possible alternate subunit interactions.
authors.affiliation: Department of Biochemistry, University of Iowa College of Medicine, Iowa City, IA 52242-1109, USA.
authors.forename: Bret D
authors.initials: BD
authors.lastname: Freudenthal
authors.forename: Lokesh
authors.initials: L
authors.lastname: Gakhar
authors.forename: S
authors.initials: S
authors.lastname: Ramaswamy
authors.forename: M Todd
authors.initials: MT
authors.lastname: Washington
mesh_terms: D001665:Binding Sites / Q000235:genetics; D003001:Cloning, Molecular; D003460:Crystallization; D018360:Crystallography, X-Ray; D004260:DNA Repair; D004261:DNA Replication; D005973:Glutamine / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D057927:Hydrophobic and Hydrophilic Interactions; D008956:Models, Chemical; D050505:Mutant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D018809:Proliferating Cell Nuclear Antigen / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding / Q000235:genetics; D011487:Protein Conformation; D055503:Protein Multimerization / Q000235:genetics; D055550:Protein Stability; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D050505:Mutant Proteins; D018809:Proliferating Cell Nuclear Antigen; D029701:Saccharomyces cerevisiae Proteins; D005973:Glutamine