Heterodimerization with the β1 subunit directs the α2 subunit of nitric oxide-sensitive guanylyl cyclase to calcium-insensitive cell-cell contacts in HEK293 cells: Interaction with Lin7a

Nitric oxide-sensitive guanylyl cyclase is a heterodimeric enzyme consisting of an alpha and a beta subunit. Two different a subunits (alpha(1) and alpha(2)) give rise to two heterodimeric enzymes alpha(1)/beta(1) and alpha(2)/beta(1). Both coexist in a wide range of tissues including blood vessels and the lung, but expression of the alpha(2)/beta(1) form is generally much lower and approaches levels similar to the alpha(1)/beta(1) form in the brain only. In the present paper, we show that the alpha(2)/beta(1) form interacts with Lin7a in mouse brain synaptosomes based on co-precipitation analysis. In HEK293 cells, we found that the overexpressed alpha(1)/beta(1) form, but not the ai/Bi form is directed to calcium-insensitive cell-cell contacts. The isolated PDZ binding motif of an amino-terminally truncated alpha(2) subunit was sufficient for cell-cell contact localization. For the full length alpha(2) subunit with the PDZ binding motif this was only the case in the heterodimer configuration with the Bi subunit, but not as isolated alpha(2) subunit. We conclude that the PDZ binding motif of the alpha(2) subunit is only accessible in the heterodimer conformation of the mature nitric oxide-sensitive enzyme. Interaction with Lin7a, a small scaffold protein important for synaptic function and cell polarity, can direct this complex to nectin based cell-cell contacts via MPP3 in HEK293 cells. We conclude that heterodimerization is a prerequisite for further protein-protein interactions that direct the alpha(1)/beta(1) form to strategic sites of the cell membrane with adjacent neighbouring cells. Drugs increasing the nitric oxide-sensitivity of this specific form may be particularly effective. (C) 2016 Elsevier Inc. All rights reserved.