The Lysine Cluster Proteins Amphoterin and HB-GAM(Heparin-Binding Growth-Associated Molecule).

Rauvala Heikki, Merenmies Jussi, Raulo Erkki, Parkkinen Jaakko, 畠中 由美子

doi:10.4052/tigg.4.513

Fractionation of proteins from perinatal rat brain was monitored with a neurite outgrowth assay. These studies resulted in the isolation of the heparin-binding proteins amphoterin(p30) and HB-GAM(p18). Cloning of the proteins from cDNA libraries of rat brain revealed highly charged, lysine-rich sequences for both proteins. In amphoterin the lysine residues are clustered to the N-terminal region, which is followed by a stretch of anionic amino acids. In HB-GAM densely spaced lysine residues are found both at the N-terminal and Cterminal end of the sequence. Amphoterin is abundantly expressed in early, embryonic rat brain and in immature cells in general. It is functionally associated with process outgrowth in developing neural cells. It binds plasminogen and tissue plasminogen activator(t-PA), and thereby effectively enhances plasminogen activation. We suggest that amphoterin targets and enhances the generation of plasmin activity, which is required for the penetration of axonal and other forms of cytoplasmic processes in tissues during development or during regeneration after tissue injury. HB-GAM is expressed later in brain and has a clearly more limited tissue distribution as compared to amphoterin. It is strongly expressed in rat brain during the perinatal developmental stage that corresponds to rapid outgrowth of axonal processes and formation of synaptic connections. We suggest that HB-GAM is an extracellular matrix-associated protein that enhances the growth and pattern formation of differentiating axons.

The Lysine Cluster Proteins Amphoterin and HB-GAM(Heparin-Binding Growth-Associated Molecule).

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