Heteromeric structures

The NMDA receptor has a heteromeric structure composed of two subunit types NRl and NR2, the latter having four subunits (NR2A-NR2D) (Fig. 10.2). Molecular genetic techniques have demonstrated that native NMDA receptors are likely to be composed of a combination of the NRl subunit (which can exist in eight different splice variants) and one or more of the four NR2 subunits which are the main determinants of functional diversity among the NMDA receptors (see Chapter 3 for further details). It has been shown that there are distinct developmental and spatial expression patterns of NMDA receptor NRl subunit splice variants and NR2 receptor subunits in the CNS. 

M Lancien, P Gadal, M Hodges. Molecular characterization of higher plant NAD-dependent isocitrate dehydrogenase evidence for a heteromeric structure by the complementation of yeast mutants. Plant J 16 325-333, 1998. 

Figure 11.9 GAB Ac receptor pharmacology and structure, (a) Various GAB Ac agonists and antagonists described in the text. Picrotoxinin is the active component of picrotoxin and also acts at GABAa receptors, (b) Presumed subunit structures of GABAc receptors. The receptors can form as homomeric assemblies of p subunits but native receptors may be heteromeric assemblies of p subunits (e.g. pi and p2) or may contain both p and y subunits...

Molecular cloning has resulted in the identification of the muscle nAChR subunits oq, (3h y, 6, and 8 and the structurally related neuronal a2 to a10 and 32 to 34. The neuronal nAChR subunits a2 to a4 can assemble with 32 or 34 and generate functional heteromeric receptors the a7 to a9... 

Figure 2.1 Diagram of nicotinic acetylcholine receptor (nAChR) structure. A top view of (A) an a7 nAChR and (B) a p2 nAChR shows that homomeric and heteromeric classes of nAChRs are both pentameric in structure. Each subunit is made up of four transmembrane domains with the M2 domain making up the ion pore. (C) A side view of the four transmembrane regions shows the N terminus, C terminus, and large M3-M4 intracellular loop that make up each nAChR subunit. The extracellular loops are available for binding to ligands and the intracellular loop is available for regulation of the nAChR by intracellular signaling proteins.

The second class of AChEs exists as heteromeric assemblies of catalytic and structural subunits. One form consists of up to 12 catalytic subunits linked by disulfide bonds to filamentous, collagen-containing structural subunits. These forms are often termed asymmetric, since the tail unit imparts substantial dimensional asymmetry to the molecule. The collagenous tail unit links by disulfide bonding at its proline rich N-terminus through a coiled coil arrangement to the C-terminus of two of the catalytic subunits [30]. The tail unit associates with the basal lamina of the synapse rather than the plasma membrane. 

Figure 6.2. Diagrammatic representation of the 5-HT3 receptor. The 5-HT3 receptor is distinct from the other 5-HT receptor subtypes, in that it is a ligand gated ion channel that is permeable to sodium and potassium. The 5-HT3 receptor is structurally similar to the nicotinic acetylcholine receptor and is composed of five sub-units. Two sub-units have been cloned, 5-HT3A and 5-HT35, and homomeric (5-HT3A) and heteromeric (5-HT3a/5-HT3b) forms of the receptor have both been...

One property of hydrophobic interactions is that they tend not to be specific. In other words (and as evident in natural coiled-coil structures), the basic coiled coil pattern HPPHPPP is compatible with a number of helix-bundle quaternary structures. Dimeric, trimeric, tetrameric, penta-meric, and dodecameric coiled coils are all known as are homomeric and heteromeric complexes and topologies with parallel, antiparallel, or mixed arrangements of helices (Burkhard et at, 2001 Gruber and Lupas,... 

Kainate receptors (KAR) are heteromeric ionotropic glutamate receptors that play a variety of roles in the regulation of synaptic network activity. KAR are composed of five different subunits designated as GluR5, GluR6, GluR7, KA1, and KA2. These subunits have molecular masses of 100 kDa. The primary structure of KA... 

Schuller, H.-J., Richter, K., Hoffmann, B., Ebbert, R., and Schweizer, E., 1995, DNA binding site of the yeast heteromeric Ino2p/Ino4p basic helix-loop-helix transcription factor Structural requirements as defined by saturation mutagenesis. FEBS Lett. 370 149-152. 

A heteromeric, as opposed to a homomeric, six-component solid-state assembly, of composition 2(thiodiglycolic acid) 4(isonicotinamde), has been described by Aakeroy et al. (Fig. 11).23 As in the case of 2(carboxylic acid) 2(amide), the central core was based on an amide dimer. The two diacids served as U-shaped units that forced two amide dimers to stack via hydrogen bonding to give the monocyclic structure. 

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