Heterophilic and homophilic cadherin interactions in intestinal intermicrovillar links are species dependent

Abstract

Enterocytes are specialized epithelial cells lining the luminal surface of the small intestine that build densely packed arrays of microvilli known as brush borders. These microvilli drive nutrient absorption and are arranged in a hexagonal pattern maintained by intermicrovillar links formed by 2 nonclassical members of the cadherin superfamily of calcium-dependent cell adhesion proteins: protocadherin-24 (PCDH24, also known as CDHR2) and the mucin-like protocadherin (CDHR5). The extracellular domains of these proteins are involved in heterophilic and homophilic interactions important for intermicrovillar function, yet the structural determinants of these interactions remain unresolved. Here, we present X-ray crystal structures of the PCDH24 and CDHR5 extracellular tips and analyze their species-specific features relevant for adhesive interactions. In parallel, we use binding assays to identify the PCDH24 and CDHR5 domains involved in both heterophilic and homophilic adhesion for human and mouse proteins. Our results suggest that homophilic and heterophilic interactions involving PCDH24 and CDHR5 are species dependent with unique and distinct minimal adhesive units.

Adhesion-based capture stabilizes nascent microvilli at epithelial cell junctions

“…Although IMAC protocadherin adhesion properties differ across species [16], previous biochemical studies established that in humans, heterophilic complexes of CDHR2 and CDHR5 exhibit strong adhesion, CDHR2 demonstrates weak homophilic adhesion, and CDHR5 demonstrates no homophilic adhesion [11]. To further study the nature of transjunctional IMACs, we developed a cell mixing approach that enabled us to drive the formation of adhesion complexes consisting of different complements of CDHR2 and/or CDHR5 ( Fig.…”

“…If so, this would offer a mechanistic explanation for the upright orientation and constrained motility that microvilli demonstrate at these sites, and potentially the long-term stabilization that enables microvillar accumulation on the apical surface in large numbers. Previous work in CACO-2 BBE cells, native mouse intestinal tissue, and X-ray crystallography all indicate that the interacting ectodomains of CDHR2 and CDHR5 are structurally capable of spanning gaps up to 63 nm wide [11, 16], suggesting that they could easily reach across the ∼15 nm tight junction between neighboring cells [37]. Indeed, in the current study, super-resolution imaging revealed that CDHR2 and CDHR5 span the intercellular space to form transjunctional IMACs that physically link marginal microvilli that extend from neighboring cells.…”

“…Previous work also identified protocadherins CDHR2 and CDHR5 as the primary adhesive elements in these links, which form trans heterophilic adhesion complexes that are well suited for bridging the ∼50 nm gap between neighboring microvilli [11, 15]. CDHR2 and CDHR5 ectodomains contain multiple extracellular cadherin (EC) repeat motifs arranged in tandem, which are anchored to the membrane via a single spanning transmembrane domain [16]. Both protocadherins also contain cytoplasmic tails at their C-termini, which enable direct interactions with cytoplasmic IMAC binding partners including the actin-based motor, myosin-7B (MYO7B), and the scaffolding proteins, ankyrin repeat and sterile alpha motif domain containing 4B (ANKS4B) and usher syndrome 1C (USH1C) [12, 13, 17, 18].…”

Isoform-specific targeting properties of the protocadherin CDHR5 control its apical delivery to promote brush border assembly

“…The emerging structural view of inner ear tip-links is that they are formed by a 2:2 complex of CDH23 and PCDH15, in which a cis -homodimer of CDH23 forms the upper portion of the tip-link and a PCDH15 cis -homodimer forms the lower portion (42-44). Sequence and structural analyses suggest that CDHR5 found in intermicrovillar adhesion links represents the ‘functional equivalent’ of PCDH15 found in inner ear tip-links (45). Detailed structural and biophysical studies showed that PCDH15 dimerizes by forming a double-helical assembly of two molecules, mediated by two independent cis -dimerization interfaces involving the EC2-EC3 domain region and a unique membrane-adjacent domain (MAD)(43,44).…”

Structure of the Harmonin PDZ2 and coiled‐coil domains in a complex with CDHR2 tail and its implications

“…In microvilli, cadherin-related family member 2 (CDHR2, also known as protocadherin-24) from one microvillus interacts with a cadherin-related family member 5 (CDHR5, also called mucin-like protocadherin) from the neighboring microvillus in a head-to-head manner to form the intermicrovillar link. 13,14 Similarly, in stereocilia, the tip link is formed by cadherin-23 (CDH23, encoded by USH1D) from the taller row and protocadherin-15 (PCDH15, encoded by USH1F) from the shorter row. 15,16 The molecular components at the cytoplasmic side of these two protrusions are also similar.…”