MukB

MukB is a bacterial protein that serves as a core component of the chromosome condensation and segregation machinery in many bacteria, most notably in Escherichia coli. It is the founding member of the bacterial condensin family and forms a functional complex with two accessory proteins, MukE and MukF (the MukBEF complex), which is essential for proper chromosome organization.

Structure and family association: MukB belongs to the structural maintenance of chromosomes (SMC) family. It is a large protein with long coiled-coil regions and a central hinge that promotes dimerization, forming a V-shaped molecule. The N- and C-terminal regions of MukB contribute to an ATPase head domain, a feature shared with other SMC proteins. In the MukBEF complex, MukF acts as a kleisin-like partner linking the MukB heads, while MukE regulates activity and stability.

Function: The MukBEF complex functions to condense and organize the bacterial chromosome, facilitating proper chromosome segregation during cell division. It helps maintain nucleoid structure, influences the positioning and separation of replicated origins, and cooperates with other chromosomal enzymes such as topoisomerases to manage DNA topology. ATP binding and hydrolysis by the MukB heads drive conformational changes that support chromosome looping and organization. The activity of MukBEF is modulated by MukE and MukF and can be influenced by interactions with other nucleoid-associated proteins.

Distribution and phenotype: MukB homologs are found in a range of bacteria, often with species-specific differences in regulation and interactions. Mutations in mukB or disruption of the MukBEF complex typically lead to chromosome missegregation, abnormal nucleoid morphology, and growth defects, underscoring the critical role of MukB in chromosome maintenance.

See also: SMC proteins, MukE, MukF, chromosome segregation, nucleoid organization.