W0115

One of the first steps in protein characterization is its molecular weight (MW) determination. This can be obtained by many different kinds of techniques such as electrophoresis, mass spectroscopy, light scattering, NMR, aminoacid sequences and others. In this work we propose another way of obtaining this information using a simple small angle X-ray scattering (SAXS) curve on an arbitrary scale. Attempts were made to use SAXS data in order to access the MW of several polymers [1] but no detailed and exhaustive work to determine the MW of macromolecules has been proposed. In this context we intend to obtain information on the MW of proteins, when they are monodisperse in solution, to a precision of grater than 90% by using SAXS. This methodology could be extended to other scattering objects like DNA, polymers, micelles, etc. We will discuss the problem together with its implications and possibilities and also some possible experimental difficulties related to them. This method might help to solve many problems related to structural biology. One practical application is the knowledge of the oligomerization state of a protein in solution which could be obtained once its biological MW unit is known. Knowledge about its oligomeric state is also related to knowledge about its biological function, due to the importance of such information for the understanding of the relationship between structure and biological function. Since proteins in solution normally behave in different ways when submitted to different physicochemical conditions (pH, concentration, temperature, etc), specially regarding their oligomerization state, the knowledge of this information becomes useful in the manipulation of these macromolecules, from their purification up to their crystallization.