Bruce W. Altrock

GDNF-induced activation of the ret protein tyrosine kinase is mediated by GDNFR-α, a novel receptor for GDNF

We report the expression cloning and characterization of GDNFR-alpha, a novel glycosylphosphatidylinositol-linked cell surface receptor for glial cell line-derived neurotrophic factor (GDNF). GDNFR-alpha binds GDNF specifically and mediates activation of the Ret protein-tyrosine kinase (PTK). Treatment of Neuro-2a cells expressing GDNFR-alpha with GDNF rapidly stimulates Ret autophosphorylation. Ret is also activated by treatment with a combination of GDNF and soluble GDNFR-alpha in cells lacking GDNFR-alpha, and this effect is blocked by a soluble Ret-Fc fusion protein. Ret activation by GDNF was also observed in cultured embryonic rat spinal cord motor neurons, a cell type that responds to GDNF in vivo. A model for the stepwise formation of a GDNF signal-transducing complex including GDNF, GDNFR-alpha, and the Ret PTK is proposed.

Control of misincorporation of de novo synthesized norleucine into recombinant interleukin-2 in E. coli

Interleukin-2 produced from a recombinant E. coli was found to contain as much as 19% norleucine in place of methionine in a minimal medium fermentation. Medium supplementation experiments and use of a leucine-requiring mutant host strain indicated the origin of norleucine to be de novo biosynthesis by reactions involving the enzymes of the leucine biosynthetic pathway. The misincorporation was highly suppressed by addition of either L-leucine or L-methionine to the fermentation and completely suppressed by adding both amino acids.