Table 2.

Comparison of CheZ_C peptide contacts with CheY

Hydrophobic interactionsa
CheY	CheZC	F432YZ200-214c	P2(1)2(1)2YZ200-214	CheY-CheZ1-2149
95Ile	200Ala	−	+d	− d
95Ile	208Leu, 209Leu	+	+	+
95Ile	212Leu	+	−	−
95Ile	205Val	+	+	+
96Ile	208Leu	+	−	−
99Ala	209Leu	−	+	+
99Ala	212Leu	+	−	−
99Ala	214Phe	−	+	− e
106Tyr	205Val	−	+	+
106Tyr	209Leu	+	−	−
106Tyr	214Phe	+	−	−
108Val	205Val	−	+	+

Hydrogen bonds b
CheY		CheZC		F432YZ200-214c	P2(1)2(1)2YZ200-214	CheY-CheZ1-2149
90Ala	O	200Ala	N	−	2.80d	− d
106Tyr	O	202Gln	Nε2	−	2.99	2.85
108Val	N	202Gln	Oε1	−	3.02	2.42
119Lys	Nζ	214Phe	O	2.78f	−	− e

Salt bridges b
CheY		CheZC		F432YZ200-214c	P2(1)2(1)2YZ200-214	CheY-CheZ1-2149
119Lys	Nζ	206Asp	Oσ1	−	3.16	2.73
119Lys	Nζ	206Asp	Oσ2	−	2.78	2.91
119Lys	Nζ	214Phe	OXT	2.78f	−	−

^aCarbon-carbon distances in the hydrophobic interactions are within 4.0 Å.

^bHydrogen bonds and salt bridge contact distances are between 2.6 Å and 3.2 Å.

^cValues are given for the BeF₃⁻-free ^F432YZ_200-214 structure solved from a crystal grown in Tris (pH 8.4). Contact distances differ marginally in the rest of the ^F432YZ_200-214 models.

^dIt is not clear if the contacts involving ²⁰⁰Ala of CheZ, observed in the ^P2(1)2(1)2YZ_200-214 structure, is physiological or an artifact of acetylating the N-terminus of CheZ_200-214 peptide. The backbone NH group of ²⁰⁰Ala should still be available for hydrogen bond interaction if the chain is not truncated at this residue, as in CheZ_1-214. However, in contrast to the other contacting residues in both CheY and CheZ, only ²⁰⁰Ala is not conserved (Figure 1). The absence of this contact in the CheY-CheZ_1-214 structure is due to the absence of ²⁰⁰Ala from the final CheY-CheZ_1-214 model⁹.

^e214Phe is not included in the final CheY-CheZ_1-214 model due to high disorder⁹.

^fThe lone electron pair on the C-terminal carboxylate group of CheZ_200-214 should exist in resonance with the carbonyl group of the C-terminal residue ²¹⁴Phe. Hence, in all the ^F432YZ_200-214 structures, the salt bridge between the positively-charged ¹¹⁹Lys sidechain and the negatively-charged C-terminus of the peptide would predominate over the hydrogen bond between the ¹¹⁹Lys sidechain and the backbone carbonyl of ²¹⁴Phe of the CheZ_200-214 peptide.