Production and characterisation of deletion mutants of ovine growth hormone

A number of analogues of ovine growth hormone (GH), in which regions of the hormone had been deleted, were produced by site-directed mutagenesis, and characterised by radioimmunoassays and radioreceptor assays. These analogues were based on a previously described variant (oGH1) in which an 8-residue extension replaces the N-terminal alanine of pituitary-derived ovine GH. Three analogues with deletions near the N-terminus were studied, with shorter extensions of 7 or 1-2 residues (oGH14, oGH5) or with the N-terminal sequence Ala-Phe-Pro- of pituitary-derived ovine GH replaced by Thr-Met-Ile-Thr- (oGH11). These modifications had little effect on potency in radioimmunoassays based on a polyclonal antibody and five different monoclonal antibodies (MABs), or in a radioreceptor assay, indicating that the N-terminal sequence was not included in the epitope binding to any of the monoclonal antibodies, or a major epitope binding to the polyclonal antibody, or in receptor binding site 1. A variant in which residues 133-139 were deleted retained full binding to 4 of the 5 MABs, suggesting correct folding, but markedly reduced binding to MAB OA16, suggesting that the epitope for this MAB includes some or all of these residues. This variant also failed to displace about 35% of labelled hormone from the polyclonal antibody studied, suggesting that residues 133-139 may be involved in a major epitope for this antibody. This variant showed slightly lower receptor binding activity than ovine GH. Two other deletion variants - oGH1Delta33-46 (equivalent to the naturally occurring 20K variant of human GH) and oGH1Delta180-191 (lacking the C-terminal 12 residues) showed poor folding efficiency and solubility, and low binding to all MABs except OA15, which has a linear epitope. The results suggest that these variants were incorrectly folded, but interestingly they did retain some activity in the receptor-binding assay (respectively about 5% and 0.5% of the activity of ovine GH itself).

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Studies on the different conditions for rabies virus neutralization by monoclonal antibodies #1-46-12 and #7-1-9

Journal of General Virology ◽

10.1099/0022-1317-83-12-3045 ◽

2002 ◽

Vol 83 (12) ◽

pp. 3045-3053 ◽

Cited By ~ 19

Author(s):

Takashi Irie ◽

Akihiko Kawai

Keyword(s):

Monoclonal Antibodies ◽

Rabies Virus ◽

Receptor Binding ◽

Binding Activity ◽

Host Cells ◽

Virus Neutralization ◽

Escape Mutant ◽

Virus Infectivity ◽

Receptor Binding Site ◽

Viral Receptor

Virus-neutralizing activity of two monoclonal antibodies (mAbs), #7-1-9 and #1-46-12, against rabies virus glycoprotein (G) was compared. Although these mAbs affected the virion’s ability to bind to host cells similarly, a big difference was found in the titres of virus neutralization (1:7132 and 1:32 for mAbs #1-46-12 and #7-1-9, respectively, at a concentration of 10 μg protein/ml). Although no big difference in virion-binding affinity between the two mAbs was found, the number of antibodies required for virus neutralization was very low, ⩽20 molecules for mAb #1-46-12 and ⩾250 molecules for mAb #7-1-9. In the latter case, the mAbs cover a major part of the virion surface and cause steric hindrance of viral receptor-binding activity. The infectivity of an epitope-preserved escape mutant virus (R-61) was not affected by the binding of high numbers of mAb #1-46-12 to the virion, which implies that mAb binding does not mask the receptor-binding site of the viral spikes. Based on these results, it is hypothesized that mAb #1-46-12 affected virus infectivity by a mechanism different from covering the virion spikes. Possible virus-neutralizing mechanisms by low numbers of mAb #1-46-12 in comparison to that of mAb #7-1-9 are discussed.

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