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The zinc-binding protein semenogelin I is the major structural component of the gelatinous coagulum that is formed in freshly ejaculated semen. Se-menogelin I is a rapidly evolving protein with a primary structure that con-sists of six repetitive units, each comprising approximately 60 amino acid residues. | ỊFEBS Journal Structural properties of semenogelin I Johan Malm1 Magnus Jonsson1 Birgitta Frohm1 and Sara Linse2 1 Department of Laboratory Medicine Section for ClinicalChemistry Lund University Malmo University Hospital Sweden 2 Department of BiophysicalChemistry Lund University Sweden Keywords fertility semen semenogelin structure zinc Correspondence M. Jonsson Department of Laboratory Medicine Section for Clinical Chemistry Lund University Malmo University Hospital SE-205 02 Malmo Sweden Fax 46 40 33 62 86 Tel 46 40 33 14 37 E-mail magnus.jonsson@med.lu.se Received 15 May 2007 revised 4 July 2007 accepted 6 July 2007 doi 10.1111 j.1742-4658.2007.05979.x The zinc-binding protein semenogelin I is the major structural component of the gelatinous coagulum that is formed in freshly ejaculated semen. Se-menogelin I is a rapidly evolving protein with a primary structure that consists of six repetitive units each comprising approximately 60 amino acid residues. We studied the secondary and tertiary structure of semenogelin I by circular dichroism CD spectroscopy and Trp fluorescence emission spectroscopy. Fitting to the far-UV CD data indicated that the molecule comprises 5-10 a-helix and 20-30 b-sheet formations. The far-UV spectrum of semenogelin I is clearly temperature dependent in the studied range 5-90 C and the signal at 222 nm increased with increasing temperature. The presence of Zn2 did not change the secondary structure revealed by the far-UV CD spectrum whereas it did alter the near-UV CD spectrum which implies that rearrangements occurred on the tertiary structure level. The conformational change induced in semenogelin I by the binding of Zn2 may contribute to the ability of this protein to form a gel. In living systems the interactions between proteins and metal ions control many central processes such as memory learning blood clotting muscle contraction and vision. Generally speaking a metal ion can play a catalytic or a stabilizing role it can induce a .
