ON THE STRUCTURE OF MICROTUBULES, TAU, AND PAIRED HELICAL FILAMENTS

Microtubules and their associated proteins form the basis of axonal tr ansport; they are degraded during the neuronal degeneration in Alzheim er's disease. This article surveys recent results on the structure of microtubules, tau protein, and PHFs. Microtubules have been investigat ed by electron microscopy and image processing after labeling them wit h the head domain of the motor protein kinesin. This reveals the arran gement of tubulin subunits in microtubules and the shape of the tubuli n-motor complex. Tau protein was studied by electron microscopy, solut ion X-ray scattering, and spectroscopic methods. It appears as an elon gated molecule (about 35 nm) without recognizable secondary structure. Alzheimer PHFs were examined by FTIR and X-ray diffraction; they, too , show evidence for secondary structure such as beta sheets.