Subunit interactions

Knight, S., Andersson, I., Branden, C.-I. Crystallographic analysis of ribulose-l,5-bisphosphate carboxylase from spinach at 2.4 A resolution. Subunit interactions and active site. /. Mol. Biol. 215 113-160,... 

In spite of the absence of the C-terminal domains, the DNA-binding domains of lambda repressor form dimers in the crystals, as a result of interactions between the C-terminal helix number 5 of the two subunits that are somewhat analogous to the interactions of the C-terminal p strand 3 in the Cro protein (Figure 8.7). The two helices pack against each other in the normal way with an inclination of 20° between the helical axes. The structure of the C-terminal domain, which is responsible for the main subunit interactions in the intact repressor, remains unknown. 

Figure 8.11 The DNA-binding domain of 434 repressor. It is a dimer in its complexes with DNA fragments. Each subunit (green and brown) folds into a bundle of four a helices (1-4) that have a structure similar to the corresponding region of the lambda repressor (see Figure 8.7) including the helix-turn-helix motif (blue and red). A fifth a helix (5) is involved in the subunit interactions, details of which are different from those of the lambda repressor fragment. The structure of the 434 Cro dimer is very similar to the 434 repressor shown here.

Figure 8.19 The a helices of the N-terminal region of the trp repressor are involved in subunit interactions and form a stable core in the middle of the dimer. Alpha helices 4-6, which include the helix-turn-helix motif, form two "head" regions at the two ends of the molecule. Alpha helix 3 connects the core to the head in both subunits. (Adapted from R.W. Schevitz et al., Nature 317 782-786, 1985.)...

Many biochemical and biophysical studies of CAP-DNA complexes in solution have demonstrated that CAP induces a sharp bend in DNA upon binding. This was confirmed when the group of Thomas Steitz at Yale University determined the crystal structure of cyclic AMP-DNA complex to 3 A resolution. The CAP molecule comprises two identical polypeptide chains of 209 amino acid residues (Figure 8.24). Each chain is folded into two domains that have separate functions (Figure 8.24b). The larger N-terminal domain binds the allosteric effector molecule, cyclic AMP, and provides all the subunit interactions that form the dimer. The C-terminal domain contains the helix-tum-helix motif that binds DNA. 

Figure 9.17 Schematic diagram illustrating the tetrameric stmcture of the pS3 oligomerization domain. The four subunits have different colors. Each subunit has a simple structure comprising a p strand and an a helix joined by a one-residue turn. The tetramer is built up from a pair of dimers (yellow-blue and red-green). Within each dimer the p strands form a two-stranded antiparallel p sheet which provides most of the subunit interactions. The two dimers are held together by interactions between the four a helices, which are packed in a different way from a four-helix bundle. (Adapted from P.D. Jeffrey et al.. Science 267 1498-1502, 1995.)...

In the T = 4 structure there are 240 subunits (4 x 60) in four different environments, A, B, C, and D, in the asymmetric unit. The A subunits interact around the fivefold axes, and the D subunits around the threefold axes (Figure 16.7). The B and C subunits are arranged so that two copies of each interact around the twofold axes in addition to two D subunits. For a T = 4 structure the twofold axes thus form pseudosixfold axes. The A, B, and C subunits interact around pseudothreefold axes clustered around the fivefold axes. There are 60 such pseudothreefold axes. The T = 4 structure therefore has a total of 80 threefold axes 20 with strict icosahedral symmetry and 60 with pseudosymmetry. 

Satellite tobacco necrosis virus is an example of a T = 1 virus structure. The 60 identical subunits interact tightly around the fivefold axes on the surface of the shell and around the threefold axes on the inside. These interactions form a scaffold that links all subunits together to complete the shell. 

Rossmann, M.G., et al. Subunit interactions in southern bean mosaic virus. J. Mol. Biol. 166 37-72, 1983. 

Role of the Amino Acid Sequence in Protein Structure Secondary Structure in Protein.s Protein Folding and Tertiary Structure Subunit Interaction.s and Quaternary Structure... 

The subunits of an oligomeric protein typically fold into apparently independent globular conformations and then interact with other subunits. The particular surfaces at which protein subunits interact are similar in nature to the interiors of the individual subunits. These interfaces are closely packed and involve both polar and hydrophobic interactions. Interacting surfaces must therefore possess complementary arrangements of polar and hydrophobic groups. 

The working hypothesis is that, by some means, interaction of an allosteric enzyme with effectors alters the distribution of conformational possibilities or subunit interactions available to the enzyme. That is, the regulatory effects exerted on the enzyme s activity are achieved by conformational changes occurring in the protein when effector metabolites bind. 

Based on the information presented in the text and in Figures 25.4 and 25.5, suggest a model for the regulation of acetyl-CoA carboxylase. Consider the possible roles of subunit interactions, phosphorylation, and conformation changes in your model. 

In NDO, the corresponding loop is much longer and does not interact with the environment of the Rieske cluster, hut is involved in subunit interactions with the catalytic domain in a neighboring subunit (11). 

Manning JM et aJ Normal and abnormal protein subunit interactions in hemoglobins.] Biol Chem 1998 273 19359-Mario N, Baudin B, Giboudeau J Qualitative and quantitative analysis of hemoglobin variants by capillary isoelectric focusing. J Chromatogr B Biomed Sci Appl 1998 706 123-Reed W, Vichinsky EP New considerations in the treatment of sickle cell disease. Annu Rev Med 1998 49 46l. 

The a subunit has two other important functional domains in addition to the P-binding domain. First, the a subunit interacts with the receptor through a domain that includes the last five amino acids of the C-terminus (Figure 7.3). Second, it bears the guanine nucleotide binding pocket and... 

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