Single-chain variable fragments (scFvs) of anti-neuraminidase antibody NC10 were constructed by joining the VH and VL domains with 10-residue (Gly4Ser)2 and five-residue (Gly4Ser) linkers; a zero-residue linker scFv was constructed by joining the C-terminal residue of the VH domain to the N-terminus of the VL domain. The scFv with the 10- and five-residue linkers exclusively formed dimeric antibody fragments (M(r) 52000). These were shown to be bivalent and were able to cross-link two neuraminidase tetramers to form a 'sandwich' type complex; each antigen combining site could also bind an anti-idiotype Fab'. The zero-residue linker scFv (M(r) 70000) was shown to form a trimer with three active antigen combining sites, each binding an anti-idiotype Fab' to yield a complex of M(r) 212000. The orientation of the combining sites in the zero-residue linker scFv, however, was such that it could not cross-link tetramers of neuraminidase. BIAcore biosensor experiments showed that the affinity of each individual antigen combining site in both the 10- and five-residue linker scFv dimers and zero-residue linker scFv trimer was essentially the same when the scFvs were immobilized onto the sensor surface. However, when the scFvs were used as the analyte, the dimeric and trimeric scFvs showed an apparent increase in binding affinity due to the avidity of binding the multivalent scFvs.

Sequential polymerase chain reaction experiments were performed to amplify a unique sequence representing a guanine nucleotide-binding protein (G-protein)-coupled receptor from rat hypothalamic cDNA. Degenerate oligonucleotides corresponding to conserved amino acids from transmembrane domains III, V, and VI of known receptors[5-HT1A, 5-HT,c, and 5-HT2; 5-HT is serotonin (5-hydroxytryptamine)] were used as primers for the sequential reactions. The resulting product was subcloned and used to screen a rat genomic library to identify a full-length clone (MR77) containing an intronless open reading frame encoding a 366-amino acid seven-transmembrane domain protein. The human homolog was isolated, and its encoded protein had 93% overall amino acid identity with the rat sequence. Within the conserved transmembrane domains, the sequences exhibit approximately 52%, 59%, 65%, and 68% amino acid identity with the known rat 5-HT1A, rat 5-HTIB, rat 5-HT1D, and human 5-HT1E receptors, respectively. MR77 was subcloned into a eukaryotic expression vector system and expressed in CosM6 cells. Studies on broken cell preparations indicate that the expressed receptor exhibits 125I-labeled d-lysergic acid diethylamide (LSD) binding that can be displaced by serotonin but not by other biogenic amines. The specific binding is displaced by the selective 5-HT1D agonist sumatriptan but not by the mixed 5-HTIA/1D agonist 5-carboxyamidotryptamine. 125I-labeled LSD binding was competitively antagonized by the ergot alkaloids methysergide and ergotamine. HeLa cells transfected with the MR77 gene exhibited inhibition of adenylate cyclase in response to serotonin. MR77 is expressed at low levels throughout the brain, with the greatest expression in the cortex, hippocampus, and striatum. MR77 thus represents a 5-HT receptor of the 5-HT1 class, and we propose that, based on the pharmacological characterization, MR77 represents an additional 5-HTlE-like receptor.Serotonin (5- In an attempt to identify other receptors that belong to the family of 5-HT receptors, we used a strategy based upon similarities shared among known members of the family. We designed highly degenerate oligonucleotides corresponding to conserved amino acid sequences in putative transmembrane domains III, V, and VI of the 5-HT1A, 5-HT,c, and 5-HT2 receptors. These oligonucleotides were used in sequential polymerase chain reactions (PCR) with rat hypothalamus cDNA as the template to generate a series ofclones. Here we report that one of these clones and its human homolog ¶ correspond to a 5-HT receptor that is more closely related in sequence to the recently cloned human S31 receptor (5-HT1E) than any previously described 5-HT receptor but clearly is a new member of the 5-HT1 receptor family. Initial pharmacological characterization of this receptor, which is negatively coupled to adenylate cyclase, is similar to but distinct from that described previously for the 5-HTlE receptor (9,12,13), and therefore we propose that MR77 belongs to a new subgroup of 5-HTlE-like r...

Single-chain variable fragments (scFvs) of anti-Lewis y hu3S193 humanized antibody were constructed by joining the V H and V L domains with either +2 residues, +1 residue, or by directly linking the domains. In addition two constructs were synthesized in which one or two C-terminal residues of the V H domain were removed (-1 residue, -2 residue) and then joined directly to the V L domain. An scFv construct in the reverse orientation with the V L joined directly to the V H domain was also synthesized. Upon transformation into Escherichia coli all scFv constructs expressed active protein. Binding activity, multimeric status, and multivalent properties were assessed by flow cytometry, size exclusion chromatography, and biosensor analysis. The results for hu3S193 scFvs are consistent with the paradigm that scFvs with a linker of +3 residues or more associate to form a non-covalent dimer, and those with a shorter linker or directly linked associate predominantly to form a non-covalent trimer and tetramer that are in equilibrium. While the association of V domains to form either a dimer or trimer/tetramer is governed by the length of the linker, the stability of the trimer/tetramer in the equilibrium mixture is dependent on the affinity of the interaction of the individual V domains to associate to form the larger Fv module.Keywords: scFv multimers; diabody; triabody; trimer; tetrabody; anti-Lewis y antibody; hu3S193Single-chain variable fragments (scFvs) were designed to link the variable heavy-chain domain (V H ) and variable light-chain domain (V L ) via a flexible peptide linker to stabilize and enhance their interaction with each other to form an antigen-binding site (Huston et al. 1991;Malby et al. 1993). Peptide linkers >12 amino-acid residues provide sufficient spatial flexibility for the V H and V L domains to associate predominantly as scFv monomers with only small amounts of higher molecular mass multimers evident (Griffiths et al. 1993;Kortt et al. 1994;Whitlow et al. 1994). Decreasing the linker length to <10 residues prevents the V domain from interacting with its attached partner and promotes the interaction of complementary V H /V L pairs from two scFv molecules to associate to form noncovalent multivalent multimers Iliades et al. 1997;Kortt et al. 1997;Pei et al. 1997;Atwell et al. 1999;Le Gall et al. 1999;Dolezal et al. 2000). The formation of scFv dimers, trimers, and tetramers by noncovalent association of tethered V domains is dependent on the length of the linker joining the domains and the orientation of the V domains in the scFv construct . In general, with linkers of 3 to 10 residues, scFv dimers (diabodies) are predominantly formed whereas trimers (triabodies) and tetramers (tetrabodies) are formed with linkers of 2 residues or less.

A single-chain antibody fragment (scFv) of the humanised monoclonal antibody, hu3S193, that reacts specifically with Le(y) antigen expressed in numerous human epithelial carcinomas was constructed. A five-residue linker joined the C-terminus of the V(H) and the N-terminus of the V(L), which prevented V-domain association into a monomeric scFv and instead directed non-covalent association of two scFvs into a dimer or diabody. The diabody was secreted into the E. coli periplasm using a heat-inducible vector, pPOW3, and recovered as a soluble, correctly processed protein, following osmotic shock or solubilised with 4 M urea from the insoluble fraction. The diabody from both fractions was isolated by a rapid batch affinity chromatography procedure, using the FLAG affinity tag to minimise degradation and aggregation. The purified diabody has an Mr of approximately 54 kDa, was stable and demonstrated similar binding activity as the parent monoclonal antibody, as measured by FACS and BIAcore analyses. The radiolabelled diabody showed a rapid tumour uptake, with fast blood clearance, proving it to be an excellent potential candidate as a tumour-imaging agent.