A FIBER OPTIC PROBE FOR MONITORING PROTEIN AGGREGATION, NUCLEATION AND CRYSTALLIZATION

Protein crystals are often experimentally grown in hanging drops in mi crogravity experiments on-board the Space Shuttle orbiter. The techniq ue of dynamic light scattering (DLS) can be used to monitor crystal gr owth processes in hanging droplets (similar to 30 mu L) in microgravit y experiments, but elaborate instrumentation and optical alignment pro blems have made in-situ applications difficult. In this paper we demon strate that such experiments are now feasible. We apply a newly develo ped fiber optic probe to various earth and space (microgravity) protei n crystallization system configurations to test its capabilities. Thes e include conventional batch (cuvette or capillary) systems, a hanging drop method in a six-pack hanging drop vapor diffusion apparatus (HDV DA), a modified HDVDA for temperature induced nucleation and aggregati on studies, and a newly envisioned dynamically controlled vapor diffus ion system (DCVDS) configuration. Our compact system exploits the prin ciples of DLS and offers a fast (within a few seconds) means of quanti tatively and non-invasively monitoring the various growth stages of pr otein crystallization. In addition to DLS capability, the probe can al so be used for performing single-angle static light scattering measure ments. It utilizes extremely low levels of laser power (a few mu W) an d essentially eliminates the usual problems associated with optical al ignment and vibration isolation. The compact probe is also equipped wi th a miniaturized microscope for visualization of macroscopic protein crystals. This new optical diagnostic system makes possible the explor ation of new ways to grow good quality crystals suitable for X-ray cry stallographic analysis and may contribute to a concrete scientific bas is for understanding the process of crystallization.