Comparison of SynCAM1/CADM1 PDZ interactions with MUPP1 using mammalian and bacterial pull‐down systems

Abstract

Background: Synaptic cell adhesion molecule 1 (SynCAM1) also known as cell adhesion molecule 1 (CADM1) is a transmembrane cell adhesion protein that operates in a variety of physiological and pathological cellular contexts, and its interaction with the PDZ signalling protein MUPP1 have been previously implicated in autism spectrum disorder (ASD). Methods:We used in vitro pull-down systems based on the bacterial and mammalian extracts to study SynCAM1/CADM1 PDZ interactions with MUPP1 at various conditions.Results: So far, the investigated interaction of SynCAM1/CADM1 with MUPP1 has been mostly attributed to an unspecified region of MUPP1 PDZ domains 1-5 or exclusively to domain 2, using a yeast two-hybrid system. We also confirmed the single interaction of native synaptosomal CADM1 with PDZ domain 2. However, in this work, using recombinant proteins overexpressed in bacteria, we found an in vitro pull-down conditions in which all first five domains and, to a much lesser extent, MUPP1 domains 7 and 11 significantly interacted with the whole C-terminal domain of SynCAM1/CADM1. These PDZ interactions were confirmed by a pull-down assay using the last seven amino acids of the SynCAM1/CADM1 PDZ motif and using two fusion partners. Multiple interactions were additionally replicated using the continuous N-terminal MUPP1 protein fragment, which included first five PDZ domains, containing either intact or mutated domain 2. Conclusions:We hypothesize that multiple interactions might exist in vivo, representing transient low-affinity interactions or alternative binding sites on MUPP1 when domain 2 is occupied or occluded by the interaction with other ligands. This newly identified interactions extend the potential genetic mutations, possibly affecting SynCAM1/CADM1/MUPP1 function. Possible reasons for the absence of some of the identified CADM1 PDZ interactions in mammalian extracts are discussed. K E Y W O R D SMUPP1, PDZ, protein interaction, pull-down assay, SynCAM1/CADM1

A Significant Difference in Core PDZ Interactivity of SARS-CoV, SARS-CoV2 and MERS-CoV Protein E Peptide PDZ Motifs In Vitro

“…In subsequent work, we decided to investigate the interactions of PDZ peptide motifs of coronaviruses with MUPP1 homologue PATJ/INAD [ 32 ], which is similar to MUPP1 associated with epithelial tight junctions through its non PDZ interaction with PALS1 [ 33 ]. Similar to MUPP1, PATJ interacted with SARS-CoV and SARS-CoV2 PDZ motif mainly through PDZ domains 2 and 3, and domain 9, which is the homologue of MUPP1 domain 11 (Fig.…”

“…In this article, we probed MUPP1 also named MPDZ protein [ 31 ] and its homologue PATJ/INAD [ 32 , 33 ] for their potential PDZ interactivity with the SARS-CoV, SARS-CoV2, and MERS-CoV protein E PDZmotifs. Our previous results showed that a core PDZ motif interactivity is relatively promiscuous, suggesting that in vivo might be switched on/off by so far unidentified allosteric structural changes of protein complexes [ 34 ].…”