Table 2.

Summary of the side chain contacts within 4.2 Å for nonpolar side chains and the aliphatic component of polar side chains in the three αTS hydrophobic clusters^a

	ILV			ACFILMPVY			ALLb
# contacts	# residues	# contacts/ residue	# contacts	# residues	# contacts/ residue	# contacts	# residues	# contacts/ residue
Cluster 1	14	8	1.8	42	12	3.5	48	13	3.7
Cluster 2	90	31	2.9	182	57	3.2	287	100	2.9
Cluster 3	20	12	1.7	85	35	2.4	144	52	2.8
Total	124	51	2.4	309	104	3.0	479	165	2.9

^aAs noted in the legend to Figure 1, the side chain contacts are calculated based on the coordinates of the α subunit of tryptophan synthase from S. typhimurium (1BKS⁶³), which shares 85% sequence identity with E. coli αTS. ILV residues are largely conserved in E. coli, except the six I/V switches: V52I (β2), I148V (loop before β5), V166I (α5), I197V (α6), V224I (α7) and L245I (loop between α8' and α8).

^bAll residues in the sequence except glycine.