Fig. 4.

Glutamine residues brace salt bridge links of the matrix network. (A) Close-up of the bonding arrangement of glutamine with the salt bridge of the matrix network that links domains 1 and 3 of Aac2p. (B) Interactions of glutamine residues with salt-bridge residues of the matrix network of Aac2p and the yeast citrate carrier Ctp1 and oxodicarboxylate carrier Odc1p. The circles represent the odd-numbered α-helices H1, H3, and H5, with the residues indicated in the one-letter amino acid code. The interdomain and intradomain polar interactions with glutamine are shown in green- and black-dashed lines, respectively, whereas the salt bridges are shown in red. The central numbers give an estimate of the strength of interaction network in terms of number of salt bridges, assuming that hydrogen bonds have about half the interaction energy of salt bridges.