Mobility of taxol in microtubule bundles.
Mobility of taxol inside microtubules was investigated using fluorescence recovery after photobleaching on flow-aligned bundles. Bundles were made of microtubules with either GMPCPP or GTP at the exchangeable site on the tubulin dimer. Recovery times were sensitive to bundle thickness and packing, indicating that taxol molecules are able to move laterally through the bundle. The density of open binding sites along a microtubule was varied by controlling the concentration of taxol in solution for GMPCPP samples. With >63% sites occupied, recovery times were independent of taxol concentration and, therefore, inversely proportional to the microscopic dissociation rate, k(off). It was found that 10k(off)(GMPCPP) approximately equal k(off)(GTP), consistent with, but not fully accounting for, the difference in equilibrium constants for taxol on GMPCPP and GTP microtubules. With <63% sites occupied, recovery times decreased as approximately [Tax](-1/5) for both types of microtubules. We conclude that the diffusion of taxol inside the microtubule bundle is hindered by rebinding events when open sites are within approximately 7 nm of each other.
Ross
Jennifer L
JL
Physics Department, University of California, Santa Barbara, California 93106-9530, USA.
Fygenson
D Kuchnir
DK
D001665:Binding Sites; D040761:Biomimetic Materials / Q000138:chemical synthesis / Q000737:chemistry*; D004058:Diffusion; D019281:Dimerization; D036681:Fluorescence Recovery After Photobleaching / Q000379:methods*; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives* / Q000737:chemistry*; D008567:Membranes, Artificial; D008870:Microtubules / Q000737:chemistry* / Q000648:ultrastructure; D009038:Motion; D017239:Paclitaxel / Q000032:analysis* / Q000737:chemistry*; D011485:Protein Binding; D014404:Tubulin / Q000031:analogs & derivatives / Q000737:chemistry
D008567:Membranes, Artificial; D014404:Tubulin; C004805:5'-guanylylmethylenebisphosphonate; D006160:Guanosine Triphosphate; D017239:Paclitaxel