Recombinant protein sequences can trigger methylation of N-terminal amino acids in Escherichia coli.

Recombinant human hemoglobin rHb1.1 has been genetically engineered with the replacement of the wild-type valine residues at all N-termini with methionine, an Asn 108 Lys substitution on the beta globins, and a fusion of the two alpha globins with a glycine linker. When rHb1.1 was expressed in Escherichia coli, methylation of the N-terminal methionine of the alpha globin was discovered. Another mutant has been engineered with the alpha globin gene coding for N-terminal methionine followed by an insertion of alanine. Characterization of expressed hemoglobin from this variant revealed a methylated N-terminal alanine that occurred through two posttranslational events: initial excision of the N-terminal methionine, followed by methylation of alanine as the newly generated N-terminus. No methylation was observed for variants expressed with wild-type valine at the N-terminus of the alpha globin. The methylation of N-terminal amino acids was attributed to a specific protein sequence that can trigger methylation of proteins expressed in E. coli. Here we demonstrate that proline at position 4 in the protein sequence of alpha globin seems an essential part of that signaling. Although N-terminal methylation has been observed previously for native E. coli proteins with similar N-terminal sequences, methylation of the recombinant globins has allowed further delineation of the recognition sequence, and indicates that methylation of heterologous proteins can occur in E. coli.

A human recombinant haemoglobin designed for use as a blood substitute.

The need to develop a blood substitute is now urgent because of the increasing concern over blood-transmitted viral and bacterial pathogens. Cell-free haemoglobin solutions and human haemoglobin synthesized in Escherichia coli and Saccharomyces cerevisiae have been investigated as potential oxygen-carrying substitutes for red blood cells. But these haemoglobins cannot be used as a blood substitute because (1) the oxygen affinity in the absence of 2,3-bisphosphoglycerate is too high to allow unloading of enough oxygen in the tissues, and (2) they dissociate into alpha beta dimers that are cleared rapidly by renal filtration, which can result in long-term kidney damage. We have produced a human haemoglobin using an expression vector containing one gene encoding a mutant beta-globin with decreased oxygen affinity and one duplicated, tandemly fused alpha-globin gene. Fusion of the two alpha-globin subunits increases the half-life of this haemoglobin molecule in vivo by preventing its dissociation into alpha beta dimers and therefore also eliminates renal toxicity.

Human monoclonal antibody with protective activity for Escherichia coli K1 and Neisseria meningitidis group B infections.

We produced human monoclonal antibody that demonstrated specific reactivity to the K1 capsule of Escherichia coli and the group B polysaccharide of Neisseria meningitidis. The antibody was nonreactive with several strains of K1- E. coli and other gram-negative bacteria. All E. coli K1 clinical isolates tested were reactive with the antibody. When assayed for in vitro opsonophagocytic ability, the antibody caused bacterial removal only in the presence of human complement and neutrophils, an observation suggesting a non-bacteriolytic, neutrophil-dependent killing mechanism. Finally, and perhaps most importantly, the antibody was highly protective for infectious disease when used prophylactically in three animal models. The data suggest a potential use for human monoclonal antibodies in preventing and/or treating infections of the blood.

Regulation of thrombospondin secretion by cells in culture.

Thrombospondin (TS), a 450,000 molecular weight glycoprotein, is released from alpha-granules of thrombin-activated platelets and is secreted and incorporated into the extracellular matrix by several cell types in culture. We have examined the effects of cell density and transformation on the production of TS in cell culture. The levels of TS, per cell, in the culture medium of endothelial cells, smooth muscle cells, and fibroblasts were greater at lower cell densities; in fibroblasts the levels of two other extracellular matrix proteins, fibronectin and collagen, were unaffected by cell density. Our evidence indicates that the higher levels of TS in the culture medium, determined for lower-density cells, were achieved by an increased secretion of the protein rather than by a reduction in degradation or incorporation into the extracellular matrix. TS production by normal and transformed WI-38 fibroblasts was the same, although the fibronectin level in the culture medium of the transformed cells was substantially decreased. These findings suggest that the production of TS by cells in culture is regulated in a different fashion from that of fibronectin or collagen.

Thrombospondin: synthesis and secretion by cells in culture.

Thrombospondin, a high molecular weight glycoprotein secreted by platelets in response to activation by thrombin, has been identified by immunofluorescence in bovine aortic endothelial cells, human foreskin fibroblasts, and human aortic smooth muscle cells. Immunofluorescence patterns were found to be similar using antisera raised to thrombospondins purified either from bovine aortic endothelial cells or from human platelets. Radioimmune precipitation of pulse-labeled cellular proteins confirmed the presence of thrombospondin in positively stained cells. A sensitive quantitative enzyme-linked immunosorbent assay (ELISA) was developed and used to determine that the accumulation of secreted thrombospondin was similar for endothelial cells and fibroblasts but was higher for smooth muscle cells. The presence of thrombospondin in a variety of cells suggests that its function may not be limited to an involvement in platelet interactions.

Inhibition of protein synthesis in vitro by procollagen-derived fragments is associated with changes in protein phosphorylation.

The NH2-terminal extension fragment (Col 1) of the pro alpha 1(I) procollagen chain selectively inhibits the translation of procollagen mRNA in a reticulocyte lysate system, whereas the reduced and alkylated fragment (AE-Col 1) and its proteolytically derived peptides inhibit the translation of all mRNAs (Hörlein, D., McPherson, J., Goh, S. H., and Bornstein, P. (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 6163-6167). The latter inhibitory function, which occurs at the level of polypeptide chain initiation, has now been shown to be associated with an increase in phosphorylation of an Mr = 94,000 protein. The time span required for observation of changes in phosphorylation and in inhibition of protein synthesis is similar. Since AE-Col 1 can serve as a substrate for casein kinase II, we suggest that phosphorylation of AE-Col 1 and its derivatives may be required for their activity.