N-terminus Of Alpha Research Articles

Receptor-induced beta gamma release from fatty acylation-deficient mutants of G alpha z.

The neuronal-specific G protein Gz is known to interact with a large variety of receptors for neurotransmitters and hormones. Fatty acylations on the N-terminus of the alpha subunit of Gz (alpha z) provide anchorage to the plasma membrane. Fatty acylation-deficient mutants of alpha z have previously been shown to exhibit altered signaling properties. Since the N-terminus of alpha z is likely to play a critical role in beta gamma binding, we examined the ability of these mutants to interact with beta gamma subunits by means of receptor-mediated stimulation of beta gamma-sensitive type II adenylyl cyclase. Our results indicate that lack of myristoylation, but not lack of palmitoylation, impaired the ability of alpha z to mediate receptor-induced release of beta gamma subunits.

Interactions of human complement component C3 with factor B and with complement receptors type 1 (CR1, CD35) and type 3 (CR3, CD11b/CD18) involve an acidic sequence at the N-terminus of C3 alpha'-chain.

Complement component C3 is a multifunctional protein that interacts with many different ligands and receptors. Several experimental approaches involving blocking Abs, proteolytic fragmentation, and synthetic peptides have been used to predict which regions in C3 are required for its various functions. We have used site-directed mutagenesis to alter specific residues in the C3 segments 730-739 and 933-942 that have been proposed to be required for the binding of factor B by C3, and have examined, within the context of the intact C3b molecule, the effect of these substitutions on the C3b-factor B interaction. Because it has been suggested that factor H and complement receptors type 1, 2, and 3 may recognize sites in C3 that partially or completely overlap those of factor B, the relevant proteolytic fragment of each mutant C3 was tested for its ability to interact with these molecules. This study clearly demonstrates that a segment near the N-terminus of the alpha'-chain, which contains the negatively charged residues 730DE and 736EE, is involved in the interactions of C3 proteolytic fragments with factor B and complement receptors type 1 and 3, but not type 2. Factor H cofactor activity was also partially affected by these mutations. In contrast, mutation of the 937KED triplet in the C3 933-942 segment had little or no effect on any of these activities.

Existence and unique N-terminal sequence of alpha II (omega) interferon in natural leukocyte interferon preparation

Human alpha interferon produced in Sendai virus-stimulated leukocytes was purified by immunosorbent affinity chromatography and subjected to subtype analysis. All subtypes in leukocyte culture supernatant were confirmed in purified preparation. One of these subtypes was reactive in Western blotting with antibody specific to alpha II (omega). N-terminal amino acid sequence analysis of this particular subtype showed addition of two amino acids to the N-terminus of alpha II predicted through cDNA studies. The apparent cleavage site for leader sequence of alpha II was different from the site common to all other alpha subtypes. This is the first report on the isolation of natural alpha II and its unique N-terminal amino acid sequence.