Related Experiment Videos
Crystal structure of the N-terminal domain of MukB: a protein involved in chromosome partitioning
F van den Ent1, A Lockhart, J Kendrick-Jones
1MRC Laboratory of Molecular Biology, Hills Road, Cambridge, CB2 2QH, UK.
Background:
The 170 kDa protein MukB has been implicated in ATP-dependent chromosome partitioning during cell division in Escherichia coli. MukB shares its dimeric structure and domain architecture with the ubiquitous family of SMC (structural maintenance of chromosomes) proteins that facilitate similar functions. The N-terminal domain of MukB carries a putative Walker A nucleotide-binding region and the C-terminal domain has been shown to bind to DNA. Mutant phenotypes and a domain arrangement similar to motor proteins that move on microtubules led to the suggestion that MukB might be a motor protein acting on DNA.
Results:
We have cloned, overexpressed and crystallized a 26 kDa protein consisting of 227 N-terminal residues of MukB from E. coli. The structure has been solved using multiple anomalous dispersion and has been refined to 2.2 A resolution. The N-terminal domain of MukB has a mixed alpha/beta fold with a central six-stranded antiparallel beta sheet. The putative nucleotide-binding loop, which is part of an unexpected helix-loop-helix motif, is exposed on the surface and no nucleotide-binding pocket could be detected.
Conclusions:
The N-terminal domain of MukB has no similarity to the kinesin family of motor proteins or to any other nucleotide-binding protein. Together with the finding of the exposed Walker A motif this observation supports a model in which the N- and C-terminal domains come together in the dimer of MukB to form the active site. Conserved residues on one side of the molecule delineate a region of the N-terminal domain that is likely to interact with the C-terminal domain.
Insights
The N-terminal domain of E. coli MukB protein, crucial for chromosome partitioning, lacks motor protein features. Its exposed nucleotide-binding motif suggests interaction with the C-terminal domain for function.
Area of Science:
- Structural biology
- Molecular genetics
- Cell biology
Background:
- MukB is a 170 kDa protein in E. coli involved in ATP-dependent chromosome partitioning.
- It belongs to the SMC protein family, sharing structural similarities with proteins that maintain chromosomes.
- MukB's N-terminal domain has a putative nucleotide-binding site, and the C-terminal domain binds DNA, suggesting motor protein activity.
Purpose of the Study:
- To elucidate the structural and functional characteristics of the N-terminal domain of MukB.
- To investigate the potential of MukB as a DNA motor protein.
Main Methods:
- Cloning, overexpression, and crystallization of the 26 kDa N-terminal domain of MukB.
- Structure determination using multiple anomalous dispersion (MAD) to 2.2 A resolution.
Main Results:
- The N-terminal domain of MukB exhibits a mixed alpha/beta fold with a central antiparallel beta sheet.
- A putative nucleotide-binding loop is exposed on the surface, and no nucleotide-binding pocket was detected.
- The N-terminal domain shows no structural similarity to kinesin motor proteins or other nucleotide-binding proteins.
Conclusions:
- The N-terminal domain of MukB does not function as a typical motor protein domain.
- The exposed Walker A motif suggests a model where N- and C-terminal domains interact to form the active site within the MukB dimer.
- Conserved residues indicate a likely interaction site between the N- and C-terminal domains for functional activity.