Low-resolution structural studies of human Stanniocalcin-1

In this study we performed a biochemical and structural analysis of STC1 with the aim of obtaining low resolution structural information about the human STC1, since structural information in this protein family is scarce. We expressed STC1 in both E. coli and insect cells using the baculo virus system with a C-terminal 6 × His fusion tag. From the latter we obtained reasonable amounts of soluble protein. Circular dichroism analysis showed STC1 as a well structured protein with 52% of alpha-helical content. Mass spectroscopy analysis of the recombinant protein allowed to assign the five intramolecular disulfide bridges as well as the dimerization Cys202, thereby confirming the conservation of the disulfide pattern previously described for fish STC1. SAXS data also clearly demonstrated that STC1 adopts a dimeric, slightly elongated structure in solution.Our data reveal the first low resolution, structural information for human STC1. Theoretical predictions and circular dichroism spectroscopy both suggested that STC1 has a high content of alpha-helices and SAXS experiments revealed that STC1 is a dimer of slightly elongated shape in solution. The dimerization was confirmed by mass spectrometry as was the highly conserved disulfide pattern, which is identical to that found in fish STC1.Stanniocalcins (STCs) represent a small family of secreted glycoprotein hormones consisting of STC1 and STC2 in which amino acid sequences are highly conserved among aquatic and terrestrial vertebrates [1-7]. However, the lack of homology with other known proteins has hampered the understanding of their functions. Initial evidence suggested that mammalian STC1 would parallel the function of fish STC1, which has been implicated in mineral homeostasis [8-10]. It is tempting to assume that the functions of STC1 and STC2 overlap at least in part, since they share high similarity in their primary amino acid sequence especially at the N-terminus and the pattern of cysteine residues is highly co