The symmetrical structure of structural maintenance of chromosomes (SMC) and MukB proteins: long, antiparallel coiled coils, folded at a flexible hinge.


Journal Article

Structural maintenance of chromosomes (SMC) proteins function in chromosome condensation and several other aspects of DNA processing. They are large proteins characterized by an NH2-terminal nucleotide triphosphate (NTP)-binding domain, two long segments of coiled coil separated by a hinge, and a COOH-terminal domain. Here, we have visualized by EM the SMC protein from Bacillus subtilis (BsSMC) and MukB from Escherichia coli, which we argue is a divergent SMC protein. Both BsSMC and MukB show two thin rods with globular domains at the ends emerging from the hinge. The hinge appears to be quite flexible: the arms can open up to 180 degrees, separating the terminal domains by 100 nm, or close to near 0 degrees, bringing the terminal globular domains together. A surprising observation is that the approximately 300-amino acid-long coiled coils are in an antiparallel arrangement. Known coiled coils are almost all parallel, and the longest antiparallel coiled coils known previously are 35-45 amino acids long. This antiparallel arrangement produces a symmetrical molecule with both an NH2- and a COOH-terminal domain at each end. The SMC molecule therefore has two complete and identical functional domains at the ends of the long arms. The bifunctional symmetry and a possible scissoring action at the hinge should provide unique biomechanical properties to the SMC proteins.

Full Text

Duke Authors

Cited Authors

  • Melby, TE; Ciampaglio, CN; Briscoe, G; Erickson, HP

Published Date

  • September 21, 1998

Published In

Volume / Issue

  • 142 / 6

Start / End Page

  • 1595 - 1604

PubMed ID

  • 9744887

Pubmed Central ID

  • 9744887

International Standard Serial Number (ISSN)

  • 0021-9525

Digital Object Identifier (DOI)

  • 10.1083/jcb.142.6.1595


  • eng

Conference Location

  • United States