Proteins at interfaces are important in many applied areas. Despite a fairly long history of study of proteins at interfaces, many of the fundamental mechanisms remain only partly understood and research on proteins at interfaces remains very important.

Studies done with circular dichroism (CD), intrinsic fluorescence, ANS binding ability and inhibitor binding capacity by Billsten et al [1] have shown that human carbonic anhydrase II (HCA II) loses a substantial part of it's native structure after adsorption to silica particles.

We have used CD and NMR to investigate the structural changes of human carbonic anhydrase I (HCA I) when it is adsorbed to silica particles. HCA I is more stable than HCA II and according to the CD-results the native structure of HCA I is preserved after 24 hours with silica particles.

By using the TROSY technique [2], we have been able to record high-resolution NMR spectra of HCA I in the presence of silica particles (diameter 6 and 9nm). A significant reduction of the intensity is observed when particles are present. We have also shown that the spectra lose intensity with time and that the native spectrum is replaced with a spectrum that indicate a 'molten globular' like state. Which is similar to what is observed for a GuHCl-titration of HCA I [3]. We can also show that this process is depending on the size of the silica particles, the transition goes faster with increasing diameter. Our previously obtained resonance assignment of HCA I [4] has enabled us to identify some amino acids that are more affected and some amino acids that seems to be less affected by the interaction. We are now evaluating these data to map the interaction between the protein and silica particle.

[1] P. Billsten, P-O. Freskgård, U. Carlsson, B-H. Jonsson and H. Elwing FEBS Letters, 1996, 402, 67.

[2] K. Pervushin, R. Riek, G. Wilder and K. Wüthrich Proc. Natl. Acad. Sci, 1997, 94, 12366.

[3] A. Kjellsson, B-H. Jonsson and I. Sethson (manuscript).

[4] I. Sethson, U. Edlund, T.A. Holak, A. Ross and B-H. Jonsson J. Biomol. NMR, 1996, 8, 417.