Homotype

Several nonconventional cadherins that contain cadherin repeats have been described but they have specific features not found in the classical cadherins [1]. The cadherin Flamingo, originally detected in Drosophila, contains seven transmembrane segments and in this respect resembles G protein-coupled receptors. The extracellular domain of Flamingo and its mammalian homologs is composed of cadherin repeats as well as EGF-like and laminin motifs. The seven transmembrane span cadherins have a role in homotypic cell interactions and in the establishment of cell polarity. The FAT-related cadherins are characterized by a large number of cadherin repeats (34 in FAT and 27 in dachsous). Their cytoplasmic domains can bind to catenins. T- (=truncated-)cadherin differs from other cadherins in that it has no transmembrane domain but is attached to the cell membrane via a glycosylpho-sphatidylinositol anchor. 

Death domain (DD) superfamily consists of structurally related homotypic interaction motifs of approximately 90 amino acids. The motifs are organized in six antiparallel amphipathic a-helices, the so-called DD fold. The four members of the super family are the death domain (DD), the death effector domain (DED), the caspase activation and recruitment domain (CARD), and the Pyrin domain. All are important mediators for the assembly of caspase activating complexes. 

PAS domains are protein domains, encompassing about 250-300 amino acids, which in higher eukaryotes function as surfaces for both homotypic interactions... 

Another genre is the so-called homotype impurity system. One example is the substance, nickelous oxide, which is a pale-green insulator when prepcired in an inert atmosphere. If it is reheated in air, or if a mixture of NiO and Li+ is reheated in an inert atmosphere, the NiO becomes a black semi-conductor. This is a classical example of the effect of defect reactions upon the intrinsic properties of a soUd. The defect reactions involved are ... 

Zhou, F.C., and Azmitia, E.C. Induced homotypic sprouting of serotonergic fibers in hippocampus. II. An immunocytochemistry study. Brain Res 373 337-348, 1986. 

Many transmembrane proteins that mediate intracellular signaling form complexes with both intra- and extracellular proteins. For example, neural cell adhesion molecules (NCAMs) are cell-surface glycoproteins (Ch. 7). The extracellular domains of NCAMs can activate fibroblast growth factor receptors when clustered by reaction with NCAM antibodies [4] or by homotypic binding to domains of adjacent cells (see Fig. 7-2). Activation was found to sequester a complex of NCAM, (31 spectrin and PKC(32 into rafts, as defined by the operational criteria discussed on p. 28. 

D Urso, D., Brophy, P. J., Staugaitis, S. M. etal. Protein zero of peripheral myelin biosynthesis, membrane insertion, and evidence for homotypic interactions. Neuron 4 449 60,1990. 

Fusion events may be homotypic or heterotypic. Homotypic fusion indicates fusion between membranes that originate from the same compartment (i.e. fusion of ER-derived vesicles to form tubular vesicular clusters, see below). Heterotypic membrane fusion indicates fusion of membranes originating from different compartments (i.e. synaptic vesicles and the plasma membrane). Triggered fusion like neurotransmitter release is typically heterotypic. 

Lawrence, B.P. and Vorderstrasse, B.A., Activation of the aryl hydrocarbon receptor diminishes the memory response to homotypic influenza virus infection but does not impair host resistance, Toxicol. Sci., 79, 304, 2004. 

As noted above, many natively unfolded proteins become folded in the presence of an appropriate interaction partner. Fungal prion domains subscribe to this paradigm whereby the partner is itself (each other) and the interaction represents homotypic polymerization into amyloid. 

Microscopic investigation of the mice from group I revealed the presence of vessel congestion, small numerous intralobular and perivenular infiltrates, moderate focal protein-hydropic degeneration combined with polymorphism of hepatocyte nuclei and inconstant lymphoid infiltration of portal tracts. Marked activation of histiomacrophage elements — hepatic macrophages must be emphasized. Homotypic moderate inflammatory alterations remained in the liver on Days 3, 5, 7 and 10. The presence of inflammatory mononuclear infiltration in the walls of central veins, typical for a viral infection, reflects a massive lesion of the vascular... 

The family study approach, particularly when employed with systematic community-based samples, is one of the most powerful strategies to minimize heterogeneity, since etiologic factors for the development of a particular disorder can be assumed to be relatively homotypic within famihes. There is a dearth of studies that have employed within-family designs to examine either phenotypic expression or some of the putative biologic factors underlying the major anxiety disorders. For example,both Perna et al. (1996,1995) and Coryell... 

Other recombinant studies showed that recombinant N-terminal and other regions of fibrillin-1 have a tendency to dimerise (Ashworth et al, 1999b Trask et al., 1999). An unpaired cysteine residue in the first hybrid domain, which contains nine cysteines, is predicted to be involved in covalently linking N-terminally-aligned fibrillin-1 molecules (Reinhardt et al., 2000b). N- and C-terminal halves of the fibrillin-1 molecule, and the N-terminal half of fibrillin-2, were shown to interact with high affinity in solid-phase and BIAcore binding assays (Tiedemann et al., 2001). However, N- and C-terminal fibrillin-2 polypeptides did not interact with each other. These data demonstrated that fibrillins can direcdy interact in an N- to C-terminal fashion to form homotypic fibrillin-1 or heterotypic fibrillin-1/fibrillin-2 microfibrils. 

In summary, the N- to C-terminal interactions may be a basis for linear fibrillin-1 assembly, while the N- and C-terminal homotypic interactions may be critical in lateral assembly. MAGP-1 may play a role in regulating N- to C-terminal linear fibrillin-1 assembly. 

In addition, several annexins have been shown to interact directly or indirectly with actin microfilaments and microtubules, thus annexins have the potential to form a structural link between the membrane and the underlying cortical cytoskeleton (reviewed in Gerke et al. 2005 Hayes et al., 2004). As well as lateral inter-annexin interactions (either homotypic or heterotypic with other types of annexin)... 

The wings extend sideways from the body domains perpendicular to the central symmetry axis of the tetramer and could participate in the binding to some receptors (see Sections 2.3 and 4). They also seem to mediate homotypic interactions, causing tetramers to assemble into flat 2D crystals, often containing large numbers of tetramers (Lunev et al. 1991). These lattices could underlie the frequently described phenomenon of a-LTX channel clusterization (Robello et al. 1987 Krasilnikov and Sabirov 1992 Filippov et al. 1994 Van Renterghem et al. 2000). 

Rainger GE, Buckley C, Simmons DL, Nash GB, Neutrophils rolling on immobilised platelets migrate into homotypic aggregates after activation, Thromb Haemost I 998 79 1 177-1 183,... 

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