X ray Crystallography and Structural Biology Services

We can carry crystallization of individual proteins or proteins bound to other protein, peptides, small molecules or nucleic acids.

At the end of a crystal structure project, a client would receive a model file in PDB format with the atomic co-ordinates, a file with the final electron density map as well as a detailed report on the experimental details for setting crystallization trials as well as cryo-freezing of the crystals, details of data collection at a synchrotron source, procedures for data processing and and a detailed analysis of the experimentally determined 3-D structure.

The primary requirement for crystallizing a protein or protein complex is pure protein. If diffracting crystals are obtained, a known structure of a homologous protein would facilitate structure determination.

Primary crystallization screening involves incubating the protein under conditions varying different physicochemical parameters such as concentration of precipitants, concentration of salts, pH and temperature. The conditions used are made by identifying conditions that have most frequently produced protein crystals. We generally screen about 800-1000 conditions during a primary screen.

Optimization screening involves varying physicochemical parameters around the promising conditions that have been identified from the primary screens.  For example, if 20% PEG8000 and 01. M Tris-HCl (pH 7.5) are identified as a missing condition, then optimization screens would be setup varying the PEG 8000 from 10 – 30% and the pH would be varied from 7.0 – 8.0.

Primary crystallization screening would require about 2-3 mg of purified protein. The protein should be 95-98 % pure as analyzed on Coomassie-blue stained gel. Another 2-3 mg of protein would be required for optimization screens and for growing crystals that will be sent to the synchrotron beamlines for data collection.