BEHAB, A NEW MEMBER OF THE PROTEOGLYCAN TANDEM REPEAT FAMILY OF HYALURONAN-BINDING PROTEINS THAT IS RESTRICTED TO THE BRAIN

Hyaluronan (HA) is a ubiquitous component of the extracellular matrix of all tissues. In the mammalian central nervous system (CNS) HA is pr esent throughout development and into adulthood. While the functions o f HA are likely to be mediated by HA-binding proteins, no cell or tiss ue specific HA-binding proteins have been reported. In an effort to ch aracterize the composition of the extracellular matrix of the CNS, we sought to identify neural HA-binding proteins. We report here the isol ation and characterization of a cDNA with a high degree of sequence ho mology to members of the proteoglycan tandem repeat (PTR) family of HA -binding proteins. Unlike other HA-binding proteins, the expression of this cDNA is restricted to the CNS. We propose the name BEHAB, Brain Enriched HyAluronan Binding protein, for this gene. The expression of BEHAB mRNA is developmentally regulated; expression is first detected in the late embryonic period and peaks during the first two postnatal weeks. In the embryo, BEHAB is expressed at highest levels in mitotica lly active cells. The sequence of BEHAB has long stretches of identity between rat and cat, suggesting that the encoded protein is functiona lly important. The size and sequence of BEHAB are consistent with the possibility that it could serve a function like link protein, stabiliz ing interactions between HA and brain proteoglycans. These observation s suggest the existence of other tissue specific HA-binding proteins.