Table 5. Active centre residues of Salmonella Typhimurium HMP kinase, B. subtilis TMP synthase and the corresponding domains of Z. mays THI3 bifunctional enzyme.

For bacterial enzymes, the residues found in the closest neighbourhood of the bound ligands in the crystal structures [32,33,39] are listed, except the residues of the putative ATP-binding site of Salmonella Typhimurium HMP kinase, modelled through its homology with other members of the ribokinase family [32]. The corresponding putative active centre residues of Z. mays THI3 domains were identified by sequence alignment with the ClustalW program and structural modelling with the use of the SWISS-MODEL server.

Active centre	Ligand	Salmonella Typhimurium	B. subtilis	Z. mays
HMP kinase	HMP	Gly11		Gly65
		Ala18		Ala72
		Asp23		Asp77
		Val42		Thr96
		Glu44		Gln98
		Met80		Met134
		Val107		Val161
		Cys213		Cys268
	ATP	Lys176		Lys230
		Asp187		Asp242
		Arg202		Arg257
		Thr211		Thr266
		Lys237		Lys292
TMP synthase	HMP-PP		Gln57	Gln373
			Arg59	Arg375
			Lys61	Lys377
			Asn92	Asn405
			Ser130	Ser444
			Lys159	Lys473
	HET-P		Thr156	Thr470
			Thr158	Thr472
			Gly188	Gly500
			Ile208	Val523
			Ser209	Ser524
	Mg2+		Asp93	Asp406
			Asp112	Asp425