ß-Microseminoprotein (MSP) is a small and stable protein with unknown function. The protein is ~90 amino acids long and contains 10 cycteines forming five disulfide bonds. It is produced, among other places, in the prostate and was originally isolated from seminal plasma. Even though MSP was first isolated from seminal plasma it has later been found to be present to the same amount in women as in men. MSP is also present in other mammals, the amino acid sequence is, however, very different from that of humans. In addition to the 10 cysteines there are only 16 identical amino acids in the proteins from human, rhesus monkey, baboon, pig, rat and mouse. Furthermore, there is no sequence similarity between MSP and any other known protein. The tree-dimensional structure of human and porcine MSP are very similar in spite of only a 50 % identity in the amino acid sequences of the two proteins. Even though the function of MSP is not known it has been found that it binds very strongly to CRISP-3, another protein with an unknown function. Based on NMR data, and the crystal structure of a close analogue to CRISP-3, we have built a model for the complex and are now trying to refine this structure using NMR data also for CRISP-3. We are also working on the structure of chicken MSP which appear to be quite different from that of human and porcine MSP.

Collaboration: Per Fernlund (Dept. of Clinical Chemistry, Lund University, Malmö)