title: Basic residue at position 14 is not required for fast assembly and disassembly kinetics in neural cadherin.
abstract: In spite of their structural similarities, epithelial (E-) and neural (N-) cadherin are expressed at different types of synapses and differ significantly in their dimerization kinetics. Recent studies proposed a transient intermediate in E-cadherin as the key requirement for rapid disassembly kinetics of the adhesive dimer. This E-cadherin intermediate comprises four intermolecular ionic and H-bonding interactions between adhesive partners. These interactions are not preserved in N-cadherin except for a basic residue at the 14th position, which could stabilize the intermediate through either H-bonding or ionic interactions with the partner protomer. To investigate the origin of the rapid dimerization kinetics of N-cadherin in the presence of calcium, studies reported here systematically test the role of ionic and H-bonding interactions in dimerization kinetics using R14S, R14A, and R14E mutants of N-cadherin. Analytical size-exclusion chromatographic and bead aggregation studies showed two primary results. First, N-cadherin/R14S and N-cadherin/R14A mutants showed fast assembly and disassembly kinetics in the calcium-saturated state similar to that of wild-type N-cadherin. These results indicate that the fast disassembly of the calcium-saturated dimer of N-cadherin does not require a basic residue at the 14th position. Second, the dimerization kinetics of N-cadherin/R14E were slow in the calcium-saturated state, indicating that negative charge destabilizes the intermediate state. Taken together, these results indicate that the basic residue at the 14th position does not promote rapid dimerization kinetics but that an acidic amino acid in that position significantly impairs dimerization kinetics.
authors.affiliation: Department of Chemistry and Biochemistry, University of Mississippi , University, Mississippi 38677, United States.
authors.forename: Nagamani
authors.initials: N
authors.lastname: Vunnam
authors.forename: Nathan I
authors.initials: NI
authors.lastname: Hammer
authors.forename: Susan
authors.initials: S
authors.lastname: Pedigo
mesh_terms: D024361:Amino Acids, Basic; D015820:Cadherins / Q000737:chemistry* / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D002850:Chromatography, Gel; D007700:Kinetics; D008863:Microspheres; D050505:Mutant Proteins / Q000737:chemistry; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D058767:Protein Unfolding; D013329:Structure-Activity Relationship; D013696:Temperature; D013997:Time Factors; D014461:Ultracentrifugation
chemical_list: D024361:Amino Acids, Basic; D015820:Cadherins; D050505:Mutant Proteins; D002118:Calcium