High Resolution Molecular Microscopy

Jeremy J. Ramsden

Abstract. Existing methods of protein structural determination either present a static picture under unnatural conditions or impose a considerable perturbation on the molecule during measurement. This chapter introduces high resolution optical waveguide lightmode spectroscopy (OWLS) as an alternative non-imaging technique of great power and versatility enabling the structure and dynamics of proteins at interfaces to be characterized with unprecedented richness and precision.

Our knowledge of the extraordinary versatility of proteins has been greatly enhanced by the combination of new experimental techniques capable of revealing structural and dynamical details with ever deeper understanding of the molecular mechanisms of processes within living organisms. Hence, "structure" can often now be correlated with "function". While these two termsarenotveryeasytodefineinafullysatisfactoryway, itcanbedoneos-tensively, an excellent example being provided by the story of haemoglobin. The peculiar features of its function, most notably its sigmoidal binding affinity for oxygen, were already known and molecular models inferred well before the details of its structure were discovered through X-ray diffraction (XRD) (e.g. Perutz 1993).

Although XRD has since become the workhorse of protein structure determination, it suffers from two significant weaknesses:

1. It presents an essentially static picture of a single structure1

2. Proteins must be present as crystals, and the exigencies of crystallization require that the proteins be placed in unusual salt conditions (good "salting out" salts (Cacace et al. 1997)).

Jeremy J. Ramsden: Department of Materials, Cranfield University, MK43 0AL, UK, E-mail: [email protected]

1 Partly mitigated by analysing the Debye-Waller factors of the diffraction pattern.

Principles and Practice Proteins at Solid-Liquid Interfaces Philippe Dejardin (Ed.) © Springer-Verlag Berlin Heidelberg 2006

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