Biological function of OM in the formation of minerals. Electrophoretic analysis of skeletal matrix proteins extracted from coralline alga L. foecundum. Lanes 1 and 2 indicate the SDS-PAGE analysis with Coomassie Brilliant Blue (CBB) staining (see Fig. S3 for full-length gel image). Lane 1 shows the protein marker, Lane 2 shows purified skeletal matrix protein as 300 kDa. Arrows indicate protein bands. Lanes 3, 4 and 5 indicate the SDS-PAGE gel with Periodic Acid-Schiff (PAS) staining (see Fig. S4 for full-length gel images). Lane 3 shows the protein marker in PAS staining. Lanes 4 and 5 demonstrate very strong glycosylation activities with two highly abundant chitin associated glycoproteins (300 kDa and 240 kDa) in algal skeletons after purification of matrix protein. SEM image A, precipitation of minerals after introducing the chitin associated glycosylation OM components in the experimental design of skeletal formation. The red arrows and yellow circles indicate aragonite and calcite minerals, respectively. Image B, AFM of skeletal minerals with both calcite (blue arrows) and needle-like aragonite (red arrows) crystals on the surface (arrows). A finely polished skeletal sample was mapped using an AFM. Image C shows an original skeletal structure in the species L. foecundum, which was most likely formed by the major components of chitin associated glycoproteins containing in the OM.