Identity of nuclear high-mobility-group protein, HMG-1, and sulfoglucuronyl carbohydrate-binding protein, SBP-1, in brain

High-mobility-group (HMG) proteins are a family of non-histone chromosomal proteins which bind to DNA. They have been implicated in multiple aspects o f gene regulation and cellular differentiation. Sulfoglucuronyl carbohydrat e binding protein, SBP-1, which is also localized in the neuronal nuclei, w as shown to be required for neurite outgrowth and neuronal migration during development of the nervous system. In order to establish relationship betw een SBP-1 and HMG family proteins, two HMG proteins were isolated and purif ied from developing rat cerebellum by heparin-sepharose and sulfatide-octyl -sepharose affinity column chromatography and their biochemical and biologi cal properties were compared with those of SBP-1. Characterization by high performance liquid chromatography-mass spectrometry (HPLC-MS), partial pept ide sequencing and western blot analysis showed the isolated HMG proteins t o be HMG-1 and HMG-2. Isoelectric focusing, HPLC-MS and peptide sequencing data also suggested that HMG-1 and SBP-1 were identical. Similar to SBP-1, both HMG proteins bound specifically to sulfated glycolipids, sulfoglucuron ylglycolipids (SGGLs), sulfatide and seminolipid in HPTLC-immuno-overlay an d solid-phase binding assays. The HMG proteins promoted neurite outgrowth i n dissociated cerebellar cells, which was inhibited by SGGLs, anti-Leu7 hyb ridoma (HNK-1) and anti-SBP-l peptide antibodies, similar to SBP-1. The pro teins also promoted neurite outgrowth in explant cultures of cerebellum. Th e results showed that the cerebellar HMG-1 and -2 proteins have similar bio chemical and biological properties and HMG-1 is most likely identical to SB P-1.