Coiled-coil proteins activity

Receptors are coiled proteins that weave in and out of the cell membrane. On the exterior surface of the receptor is a specialized area to which the neurotransmitter binds. When enough receptors are activated by the neurotransmitter, the nerve cell becomes activated and thus propagates the nerve impulse. Neurotransmitters, then, are chemical substances capable of binding to receptors, activating them, and resulting in the generation of an action potential— that is, in essence, they are capable of turning on the adjacent cell. 

Pacheco-Rodriguez et al, 1998 Vitale et al., 2000). Interaction with the ARF domain of ARDl required lysine 91 in the cytohesin-1 See domain (Vitale et ai, 2000), which is not within the sequences (motifs 1 and 2) that are critical for GEP activity. The 64-kDa ARD-1 was discovered and cloned because of its C-terminal 18-kDa ARF domain (Mishima et al., 1993). Its GTPase-activating domain was later recognized (Vitale et al., 1996). The molecular structure of ARDl identified it as a member of the TRIM (Tripartite motif) or RBCC (RING, B-Box, coiled-coil) protein family and Vichi et ai, (2005) demonstrated E3 ubiquitin ligase activity in the N-terminal part of the molecule. 

Conformational changes may also be detected by c.d. The denaturation of a-lactalbumin with guanidinium hydrochloride was studied by Kuwajima. The unfolding process, which involves three stages with an a-helical intermediate state, was followed by c.d. and difference spectra. Similarly, Takahashi et al. noted that disulphide-reduced ribonuclease A had a c.d. spectrum different from either the native or random coil protein. The reoxidation of the reduced enzyme (which results in recovery of activity) was followed by c.d. and it was shown that the change in a-helix was more rapid than that in j -structure. 

Nonrepetitive but well-defined structures of this type form many important features of enzyme active sites. In some cases, a particular arrangement of coil structure providing a specific type of functional site recurs in several functionally related proteins. The peptide loop that binds iron-sulfur clusters in both ferredoxin and high potential iron protein is one example. Another is the central loop portion of the E—F hand structure that binds a calcium ion in several calcium-binding proteins, including calmodulin, carp parvalbumin, troponin C, and the intestinal calcium-binding protein. This loop, shown in Figure 6.26, connects two short a-helices. The calcium ion nestles into the pocket formed by this structure. 

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