title: Impact of pH on the structure and function of neural cadherin.
abstract: Neural (N-) cadherin is a transmembrane protein within adherens junctions that mediates cell-cell adhesion. It has 5 modular extracellular domains (EC1-EC5) that bind 3 calcium ions between each of the modules. Calcium binding is required for dimerization. N-Cadherin is involved in diverse processes including tissue morphogenesis, excitatory synapse formation and dynamics, and metastasis of cancer. During neurotransmission and tumorigenesis, fluctuations in extracellular pH occur, causing tissue acidosis with associated physiological consequences. Studies reported here aim to determine the effect of pH on the dimerization properties of a truncated construct of N-cadherin containing EC1-EC2. Since N-cadherin is an anionic protein, we hypothesized that acidification of solution would cause an increase in stability of the apo protein, a decrease in the calcium-binding affinity, and a concomitant decrease in the formation of adhesive dimer. The stability of the apo monomer was increased and the calcium-binding affinity was decreased at reduced pH, consistent with our hypothesis. Surprisingly, analytical SEC studies showed an increase in calcium-induced dimerization as solution pH decreased from 7.4 to 5.0. Salt-dependent dimerization studies indicated that electrostatic repulsion attenuates dimerization affinity. These results point to a possible electrostatic mechanism for moderating dimerization affinity of the Type I cadherin family. Extrapolating these results to cell adhesion in vivo leads to the assertion that decreased pH promotes adhesion by N-cadherin, thereby stabilizing synaptic junctions.
authors.affiliation: Department of Chemistry and Biochemistry, University of Mississippi , University, Mississippi 38677, United States.
authors.forename: Jared M
authors.initials: JM
authors.lastname: Jungles
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Dukes
authors.forename: Nagamani
authors.initials: N
authors.lastname: Vunnam
authors.forename: Susan
authors.initials: S
authors.lastname: Pedigo
mesh_terms: D015820:Cadherins / Q000737:chemistry* / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D055503:Protein Multimerization; D055550:Protein Stability; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D058767:Protein Unfolding; D013696:Temperature
chemical_list: D015820:Cadherins; D002118:Calcium