Biopolymers and cell. 2000; 16 (5): 369 - 379

Detection and characterization of protein oligomeric species by light scattering methods: myosin light chain kinase supramolecular structures

A. M. Filenko

Modern multi-angle light scattering, fast protein liquid chromatography and laser correlation spectroscopy used together give rather complete information about the distribution of different protein particles in solution and their characteristics. The data received by these methods on smooth muscle myosin light chain kinase (MLCK) as the object of investigation suggest that MLCK exists in solution as a mixture of oligomeric, dimeric and monomeric particles which contents at ionic strength close to physiological constitute 2, 53 and 45 wt. % correspondingly. An important point is that supramolecular kinase species content in eluate from a gel filtration column was much higher than their content at equilibrium. The contributions of oligomer, dimer and monomer in eluate at the exit from the column were 5.3, 81.5 and 13.2 wt. % accordingly. All three kinase species are characterized by prolonged lifetime. The transition from pure dimer into equilibrium state lasts for about 10 min. The kinase dimer is a rod-like structure with molecular mass of about 2-10 kDa and root mean square (RMS) radius Rt 22 nm. Oligomer is characterized by RMS radius Rs 80 nm. Its structure may be presented as a helical ring containing JO kinase molecules per turn with a number of turns about 10. Another more realistic explanation of the data obtained involves a rod-like or elongated spiral model according to which 6 kinase molecules, arranged in line or elongated spiral, form one structural unit, which must be a real oligomer (hexamer). About 17 such structural units, associated in parallel, form aggregates with molecular mass of about 101 kDa. Kinase spiral hexamer fits well the structure of smooth myosin filament with which the kinase is in close contact in vivo. Preliminary experiments with a number of other proteins (myosin, myosin subfragment 1, bovine serum albumin, chemotrypsin, papain) showed that all of them form supramolecular structures with prolonged time of transition from pure species to equilibrium distribution of monomers and supramolecular structures.