CLONING AND SEQUENCE DETERMINATION OF RAT DENTIN SIALOPROTEIN, A NOVEL DENTIN PROTEIN

Dentin sialoprotein (DSP) is a 53-kDa protein isolated from rat dentin . It contains 29.6% carbohydrate (including 9% sialic acid) and has an overall composition similar to that of the bone sialoproteins osteopo ntin and bone sialoprotein (i.e. rich in Asp, Ser, Glu, and Gly). Usin g a monospecific anti-DSP polyclonal antibody to screen a rat incisor odontoblast cDNA library, a cDNA clone was isolated and sequenced. Thi s approximately 750-base pair clone contained a DNA sequence correspon ding to the NH2-terminal 9 amino acids of DSP. A second cDNA clone was isolated by using the first cDNA as a probe to rescreen the library. This second clone had the full-length DSP coding region. From the sequ ence, we deduced that the DSP cDNA coded for 366 amino acids, predomin antly Asp, Ser, Glu, and Gly. The amino acid composition calculated fo r this sequence was very similar to that for purified DSP reported ear lier; likewise the deduced molecular weight (53,045) was essentially i dentical to that determined by sedimentation equilibrium. Six potentia l N-linked glycosylation sites were present in the predicted DSP seque nce. No Arg-Gly-Asp sequence was found, and the sequence for DSP was d issimilar to those of osteopontin and bone sialoprotein. Multiple tran scripts near 4.6 and 1.5 kilobases were detected by Northern blot anal ysis in the incisor of 21-day-old rat and the tooth germ of the newbor n rat. Consistent with previous immunohistochemical findings, no trans cripts were detected in brain, salivary gland, heart, muscle, spleen, kidney, intestine, lung, liver, pancreas, tibia, calvaria, or osteobla st-like osteosarcoma (ROS 17/2.8) cells, indicating that DSP is specif ically expressed by odontoblasts and related cells.