PMID:9744887
| Citation |
Melby, TE, Ciampaglio, CN, Briscoe, G and Erickson, HP (1998) The symmetrical structure of structural maintenance of chromosomes (SMC) and MukB proteins: long, antiparallel coiled coils, folded at a flexible hinge. J. Cell Biol. 142:1595-604 |
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| Abstract |
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. |
| Links | |
| Keywords |
Bacterial Proteins/chemistry; Bacterial Proteins/ultrastructure; Chromosomal Proteins, Non-Histone; Chromosomes, Bacterial/chemistry; Chromosomes, Bacterial/ultrastructure; Escherichia coli Proteins; Nuclear Proteins/chemistry; Nuclear Proteins/ultrastructure; Protein Folding |
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