Nectin
Nectins and Nectin-like molecules (Necl) are families of cellular adhesion molecules involved in Ca2+-independent cellular adhesion.
Nectins are ubiquitously expressed and have adhesive roles in a wide range of tissues such as the adherens junction of epithelia or the chemical synapse of the neuronal tissue.
So far four nectins have been identified in humans, namely nectin-1, nectin-2, nectin-3 and nectin-4. These four family members have also been found in most other well studied mammals. Also, five Necls have been identified, these are: Necl-1, Necl-2, Necl-3, Necl-4 and Necl-5.
All nectins and all Necls share the same overall structure defined by three extra cellular immunoglobulin domains, a single transmembrane helix and an intracellular domain. For all nectins the intracellular domain can bind a scaffold protein named afadin (the product of the MLLT4 gene).
All nectins and Necls can form homo-cis dimers, meaning a dimer of two alike molecules on the same cell membrane. Following the homo-dimer formation they can trans-interact in an either heterophilic or homophilic manner. The network of the nectin and Necl trans-interactions has been characterized. Recent structural reports reveal the physical and chemical determinants of homophilic interactions mediated by N-terminal IgV domains. In general, heterophilic interactions among nectins have higher affinity than their respective homophilic interactions.
Nectins and Necls can also recruit cadherins to enhance binding.
Since the research of nectins has been approached from several angles there is still some controversy about the names of these proteins and the genes encoding them. The idea of grouping these proteins into nectins and Necls originates from Dr. Youhsimi Takais early studies of the proteins. Nectins and Necls are much related in function and protein structure and have been found to interact in a variety of way, which it is why it makes good sense to define them as families. However, if you consider the sequence of the genes encoding the proteins an alternative way of naming the proteins also make sense as pointed out by Thomas Biederer. Alternative names for nectins and Necls are listed below.
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