The F1-V vaccine antigen, protective against Yersinia pestis, exhibits a strong tendency to multimerize that affects larger-scale manufacture and characterization. In this work, the sole FIN cysteine was replaced with serine by site-directed mutagenesis for characterization of FIN non-covalent multimer interactions and protective potency without participation by disulfide-linkages. FIN and F1-V-C424S proteins were overexpressed in Escherichia coli, recovered using mechanical lysis/pH-modulation and purified from urea-solubilized soft inclusion bodies, using successive ion-exchange, ceramic hydroxyapatite, and size-exclusion chromatography. This purification method resulted in up to 2 mg/g of cell paste of 95% pure, mono-disperse protein having <= 0.5 endotoxin units per mg by a kinetic chromogenic limulus amoebocyte lysate reactivity assay. Both F1-V and F1-V-C424S were monomeric at pH 10.0 and progressively self-associated as pH conditions decreased to pH 6.0. Solution additives were screened for their ability to inhibit FIN self-association at pH 6.5. An L-argmine buffer provided the greatest stabilizing effect. Conversion to > 500-kDa multimers occurred between pH 6.0 and 5.0. Conditions for efficient F1-V adsorption to the cGMP-compatible alhydrogelo adjuvant were optimized. Side-by-side evaluation for protective potency against subcutaneous plague infection in mice was conducted for F1-V-C424S monomer; cysteine-capped FIN monomer; cysteine-capped F1-V multimer; and a F1-V standard reported previously. After a two-dose vaccination with 2 x 20 mu g of F1-V, respectively, 100%, 80%, 80%, and 70% of injected mice survived a subcutaneous lethal plague challenge with 10(8) LD50 Y pestis CO92, Thus, vaccination with FIN monomer and multimeric forms resulted in significant, and essentially equivalent, protection. Published by Elsevier Inc.