Recombinant Mouse Mimecan Protein, CF

Mimecan is a 34 kDa secreted monomeric glycoprotein that belongs to the SLRP, or small leucine-rich proteoglycan family of matrix molecules (1, 2). All SLRP family members contain multiple leucine rich repeats, of which there are two types; a 21 amino acid (aa) proline-containing S-type, and a 26 aa phenylalanine-containing T-type (2, 3). Mimecan is a class III SLRP subfamily member, which means it contains an S-T (vs. S-T-T) repeating motif. Mouse Mimecan is synthesized as a 298 aa precursor that contains a 19 aa signal sequence and a 279 aa mature region (3, 4). The mature region contains a 75 aa N-terminus followed by a 13 aa cysteine-rich region and seven consecutive LRR repeats. There is one (presumably occupied) C-terminal N-linked glycosylation site and a potential keratan sulfate attachment point in LRR #4 (aa 161 - 180) (3). Nomenclature for the mimecan molecule is confusing. Mimecan is best thought of as being the full-length, 279 aa glycoprotein (5). Proteolytic removal of the first 56 aa by BMP-1/Tolloid-like proteinases generates the 25 kDa KSPG form (aa 57 - 279) (3). The 17 kDa, 56 aa mature N-terminus has been referred to as the minecam prosegment (3). When the prosegment is removed, mature mouse KSPG (aa 57 - 279) is 98%, 91%, 90% and 91% aa identical to rat, bovine, human and canine KSPG, respectively. A 12 kDa form (aa 175 - 279) consisting of the 105 aa of the C-terminus (OIF/osteoglycan) has also been observed (6). Noncoding alternate splice forms for mouse are believed to exist and should be expressed in a tissue specific fashion (7, 8). No splice forms are known that impact the coding region. Mimecan seems to exist as proteoglycan (PG) and non-PG forms. In cornea, keratan sulfate is present, although the exact function of the PG is unknown. The corneal extracellular matrix is normally transparent. While mimecan is reported to inhibit fibrillogenesis, possibly by limiting lateral accretion of collagen monomers, it is unclear if the mimican PG actually contributes to transparency (3, 9). In other tissues, mimecan and its derivatives can exist as simple glycoproteins, absent of any PG adduct (6). The uncertain nature of mimecan’s structure and function gives rise to its name: Mime is a Norse-legend dwarf that was notoriously deceitful and misleading (6).