An amplification technology for improving sensitivity when measuring components in biological samples.

A new technology for improving the sensitivity in measuring components in biological samples is described. The method is based on the use of spherical microbeads (detection beads) which contain a large amount of immobilized enzyme and a reagent with biospecific affinity for the component to be detected. These microbeads have been used in a 'sandwich reaction' for visualization of P-fimbriated Escherichia coli which has a known receptor structure (Gal(alpha 1-4)Gal(beta)). In the initial step the bacteria were enriched on a solid support (e.g., a plastic film or beads (greater than 150 microns)) to which the receptor structure had been covalently bound. In the next step detection beads coupled with enzyme and receptor structure were added and finally a chromogenic substrate for the enzyme was used for visualization. A sensitivity of 10(5) bacteria/ml was reached. The detection beads are of general utility and might be useful for the detection of lectins on other pathogens.

Domain structure of vitronectin. Alignment of active sites.

The structure of vitronectin, an adhesive protein isolated from human plasma, was studied by chemical fragmentation. Partial cleavage of vitronectin with cyanogen bromide in 70% formic acid generated four main fragments with masses of 53,000, 43,000, 35,000, and 12,000 daltons arising from both the 75- and 65-kDa vitronectin polypeptides and a 10-kDa fragment arising only from the 75-kDa polypeptide. By varying the reaction conditions, four BrCN cleavage sites and one acid cleavage site could be identified. The latter site gave rise to 40-, 32-, and 26-kDa fragments. The order of these fragments within the vitronectin polypeptides was determined by comparison of the NH2-terminal sequences of the polypeptides and their fragments, by further cleavage of the largest fragments with BrCN or 70% formic acid, and by assaying for heparin-binding and cell-attachment activities. The NH2-terminal sequences of the intact vitronectin polypeptides are the same and identical to a 44-amino acid serum peptide called somatomedin B, indicating that vitronectin may be the precursor of somatomedin B. The cell-attachment site appears to be located within approximately 5 kDa of the NH2 terminus, but it is distinct from the somatomedin B domain. The heparin-binding site is contained in the 12-kDa fragment near the COOH terminus. This fragment was shown to bind to a chondroitin sulfate proteoglycan in addition to heparin. The NH2-terminal amino acid sequence of this glycosaminoglycan-binding fragment is remarkably rich in basic amino acids. The NH2-terminal sequences of this and the other vitronectin fragments showed no homology with the amino acid sequence of the heparin-binding domain of fibronectin or other known sequences from fibronectin. These results show that the biological activities of vitronectin are located in distinct parts of both of the vitronectin polypeptides, which appear to be identical except for the presence of an additional 10-kDa fragment near or at the COOH terminus of the 75-kDa polypeptide.

Serum spreading factor (vitronectin) is present at the cell surface and in tissues.

Monoclonal antibodies were prepared against a cell attachment-promoting protein, serum spreading factor, which had been partially purified from human serum by chromatography on glass bead columns. The antibodies selected were those that reacted with polypeptides that had cell attachment-promoting activity after sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Immunochromatography of human plasma on columns containing the monoclonal antibodies followed by affinity chromatography on heparin-Sepharose yielded material that in sodium dodecyl sulfate/polyacrylamide gel electrophoretic analysis gave polypeptides of molecular mass 65 and 75 kilodaltons. Both polypeptides bound each of three monoclonal antibodies and had cell attachment-promoting activity after transfer to nitrocellulose filters. Immunofluorescent staining of tissues with the monoclonal antibodies revealed a fibrillar pattern that was mostly associated with loose connective tissue and overlapped with fibronectin fibrils. Fetal membrane tissue, which showed strong staining with the antibodies in immunofluorescence, also gave 65- and 75-kilodalton polypeptides with cell attachment-promoting activity after chromatography on columns containing the monoclonal antibodies. One source of the tissue protein may be fibroblastic cells, because cultured human fibroblasts also stained with the monoclonal antibodies. The staining was fibrillar and appeared to be associated with the cell surface extracellular matrix. We propose the name "vitronectin" for the various forms of this protein, on the basis of its binding to glass and its adhesive properties.