Search PubMed⌕ Search

Biomedical subjects

R Sakowicz

Publications and source records attributed to R Sakowicz.

8 recordsLinked to original sources
PubMed2001

Crystal structure of the mitotic spindle kinesin Eg5 reveals a novel conformation of the neck-linker.

Success of mitosis depends upon the coordinated and regulated activity of many cellular factors, including kinesin motor proteins, which are required for the assembly and function of the mitotic spindle. Eg5 is a kinesin implicated in the formation of the bipolar spindle and its movement prior to and during anaphase. We have determined the crystal structure of the Eg5 motor domain with ADP-Mg bound. This structure revealed a new intramolecular binding site of the neck-linker. In other kinesins, the neck-linker has been shown to be a critical mechanical element for force generation. The neck-linker of conventional kinesin is believed to undergo an ordered-to-disordered transition as it translocates along a microtubule. The structure of Eg5 showed an ordered neck-linker conformation in a position never observed previously. The docking of the neck-linker relies upon residues conserved only in the Eg5 subfamily of kinesin motors. Based on this new information, we suggest that the neck-linker of Eg5 may undergo an ordered-to-ordered transition during force production. This ratchet-like mechanism is consistent with the biological activity of Eg5.

Adenosine Diphosphate↗
PubMed1999

Cloning and expression of kinesins from the thermophilic fungus Thermomyces lanuginosus.

The motor domain regions of three novel members of the kinesin superfamily TLKIF1, TLKIFC, and TLBIMC were identified in a thermophilic fungus Thermomyces lanuginosus. Based on sequence similarity, they were classified as members of the known kinesin families Unc104/KIF1, KAR3, and BIMC. TLKIF1 was subsequently expressed in Escherichia coli. The expression level was high, and the protein was mostly soluble, easy to purify, and enzymatically active. TLKIF1 is a monomeric kinesin motor, which in a gliding motility assay displays a robust plus-directed microtubule movement up to 2 microm/s. The discovery of TLKIF1 also demonstrates that a family of kinesin motors not previously found in fungi may in fact be used in this group of organisms.

Adenosine Triphosphatases↗
PubMed1998

A marine natural product inhibitor of kinesin motors.

Members of the kinesin superfamily of motor proteins are essential for mitotic and meiotic spindle organization, chromosome segregation, organelle and vesicle transport, and many other processes that require microtubule-based transport. A compound, adociasulfate-2, was isolated from a marine sponge, Haliclona (also known as Adocia) species, that inhibited kinesin activity by targeting its motor domain and mimicking the activity of the microtubule. Thus, the kinesin-microtubule interaction site could be a useful target for small molecule modulators, and adociasulfate-2 should serve as an archetype for specific inhibitors of kinesin functions.

Adenosine Diphosphate↗
PubMed1997

CENP-E is a plus end-directed kinetochore motor required for metaphase chromosome alignment.

Mitosis requires dynamic attachment of chromosomes to spindle microtubules. This interaction is mediated largely by kinetochores. During prometaphase, forces exerted at kinetochores, in combination with polar ejection forces, drive congression of chromosomes to the metaphase plate. A major question has been whether kinetochore-associated microtubule motors play an important role in congression. Using immunodepletion from and antibody addition to Xenopus egg extracts, we show that the kinetochore-associated kinesin-like motor protein CENP-E is essential for positioning chromosomes at the metaphase plate. We further demonstrate that CENP-E powers movement toward microtubule plus ends in vitro. These findings support a model in which CENP-E functions in congression to tether kinetochores to dynamic microtubule plus ends.

Amino Acid Sequence↗
PubMed1993

Threonine 246 at the active site of the L-lactate dehydrogenase of Bacillus stearothermophilus is important for catalysis but not for substrate binding.

Threonine 246 is an active site residue that is conserved in all known L-lactate dehydrogenase (LDH; EC 1.1.1.27) sequences. In order to investigate the role of Thr246 in Bacillus stearothermophilus LDH, this residue was altered by site-directed mutagenesis to valine, alanine, leucine, and serine, respectively. The effects of these mutations, as observed in both steady-state and single-turnover kinetic measurements with different substrates, demonstrated the importance for catalysis of a hydroxyl group in the 246 amino acid residue. In contrast, no significant contribution of the OH group of Thr246 to productive pyruvate binding was observed. Instead, it is proposed that the role of Thr246 may be to facilitate hydride transfer from the nicotinamide ring of the NADH cofactor to the pyruvate carbonyl group.

Base Sequence↗
PubMed1992

THR246 mutations decrease substrate inhibition in lactate dehydrogenase.

Threonine 246 in Bacillus stearothermophilus L-lactate dehydrogenase has been changed to valine, serine, and alanine by site-directed mutagenesis. Kinetic analyses show a decrease in substrate inhibition for pyruvate reduction with the T246S mutant and virtual elimination of substrate inhibition for the T246A and T246V mutants. The results indicate that the absence of substrate inhibition in the 246A/V-catalyzed reactions is due to the elimination of a key hydrogen bond between the hydroxyl group of threonine and pyruvate in the wild-type complex that is an important contributor in the formation of the abortive enzyme-NAD(+)-pyruvate complex responsible for substrate inhibition.

Escherichia coli↗
PubMed1990

Site-specific modification or rabbit muscle aldolase with fluorescent probes.

The site-specific modification of rabbit muscle aldolase A by labeling of thiol residues of Cys-289 with 5-(2-((iodoacetyl)amino)ethyl)amino)naphthalene-1-sulfonic acid and Cys-239 with 5-iodoacetamidofluorescein or 4-dimethylamino-phenylazophenyl-4'-maleimide has been described. The method is based on the differences in kinetics of the chemical modification of aldolase thiols with the above reagents either in the presence or in the absence of a competitive inhibitor. The spectral properties of the doubly labeled aldolase derivatives were compared with those of the singly labeled enzyme. The doubly labeled aldolase derivatives exhibited full catalytic activity.

Animals↗