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On the distribution of protein refractive index increments

Monday, October 24, 2011 — Poster Session I

Noon – 2:00 p.m.

Natcher Conference Center




  • P Schuck
  • P Brown
  • H Zhao


The protein refractive index increment, dn/dc, is an important parameter underlying the concentration determination and the biophysical characterization of proteins and protein complexes in many techniques. We examine the widely used assumption that most proteins have dn/dc values in a very narrow range, and re-appraise the prediction of dn/dc of unmodified proteins based on their amino acid composition. Applying this approach in large scale to the entire set of known and predicted human proteins, we obtain, for the first time, an estimate of the full distribution of protein dn/dc values. The distribution is close to Gaussian with a mean of 0.190 ml/g and a standard deviation of 0.003 ml/g. However, small proteins < 10 kDa exhibit a larger spread, and almost 3,000 proteins have values deviating by more than two standard deviations from the mean. Due to the widespread availability of protein sequences and the potential for outliers, the compositional prediction should be convenient and provide greater accuracy than an average consensus value for all proteins. We discuss how this approach should be particularly valuable for certain protein classes where a high dn/dc is coincidental to structural features, or may be functionally relevant such as in proteins of the eye.

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