N-terminal extracellular segments

Pease JE, Wang J, Ponath PD, Murphy PM. The N-terminal extracellular segments of the chemokine receptors CCR1 and CCR3 are determinants for MIP-lalpha and... 

Pease, J.E., Wang, J., Ponath, P.D., and Murphy, P.M. (1998) The N-terminal extracellular segments of the chemokine receptors CCRl and CCR3 are determinants for MIP-la and eotaxin binding, respectively, but a second domain is essential for receptor activation. The Journal of Biological Chemistry, 273, 19972-19976. 

These interactions involve adhesion proteins called selectins, which are found both on the rolling leukocytes and on the endothelial cells of the vascular walls. Selectins have a characteristic domain structure, consisting of an N-terminal extracellular lectin domain, a single epidermal growth factor (EGR) domain, a series of two to nine short consensus repeat (SCR) domains, a single transmembrane segment, and a short cytoplasmic domain. Lectin domains, first characterized in plants, bind carbohydrates... 

Selectins constitute a family of mammalian, carbohydrate-binding membrane ycoproteins present in leukocytes and endothelium. Three members of the family are well characterized leukocyte homing receptor (LAM-1, L-selectin), endothelial leukocyte adhesion molecule (ELAM-1, E-selectin), and CD62 (P-selectin) of platelets. All three have an N-terminal extracellular domain of 117-120 amino acid residues, which is responsible for Ca -dependent carbohydrate recognition. This is followed by an epidermal owth factor-like domain of 34-40 amino acids, in turn followed by variable numbers of 62-amino acid consensus repeats. There is then a transmembrane segment and a cytoplasmic domain. 

The nAChR is comprised of five subunits, each of which spans the lipid bilayer to create a water-filled pore or channel (Fig. la). Each subunit consists of four transmembrane segments, the second transmembrane segment (M2) lines the ion channel (Fig. lb). The extracellular N-terminal domain of every subunit... 

The protease activated receptors PAR-1 to PARA, of which PAR-1 is the thrombin receptor and PAR-2 conceivably a Factor-VIIa receptor, are particularly interesting cases. The ligands for these receptors are part of the N-terminal extension of the receptor. The enzyme (for example, thrombin) will bind and cleave off most of this extracellular segment and thereby reveal a new,... 

One of the most striking features of the rhodopsin structure is the complexity and compactness of a helix bundle cap or plug formed from the extracellular interhelix loops and N-terminal segment (19). Together, the N-terminal... 

Fig. 3. Architecture of ionotropic glutamate receptors. A single subunit is formed by three transmembrane domains, a membrane-reentering loop and an extended amino terminal domain (ATD). The N-terminal portion of ATD is homologous to LIVBP. The C-terminal portion of ATD and the S2 segment of the extracellular loop are homologous to LAOBP and constimte the ligand-binding domain.

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