Table 4.

Specific interactions made by ALDH homo- and heterotetramers^a.

Trimer	Monomer	β5 sheet			αG helix							β18 sheet				β19 sheet			H-bond interactions by subunit
		141	142	143	251	254	255	257	258	259	260	449	451	453	454	490	492	494	B	C	D	total
ALDH2	ALDH2	P	P	P	P	P			P	P	P	P	P	P		P	P	P	68	19	28	115
ALDH2	ALDH2*2	P	P	P	P	P			P	P	P	P	P	P		P	P	P	65	15	33	113
ALDH1B1	ALDH1B1	P	P	P	P		P		P	P	P	P	P	P		P	P	P	65	5	32	102
ALDH1B1	ALDH2	P		P	P	P			P	P	P	P	P	P	P	P	P	P	61	8	37	106
ALDH1B1	ALDH2*2	P		P	P	P	P	P	P	P	P	P	P	P		P	P	P	66	16	30	112
Residue in ALDH2		GLY	LYS	THR	ARG	GLN	LYS	ALA	GLY	SER	SER	GLY	VAL	VAL	ASN	THR	THR	LYS
Conserved residue		Y	Y	Y	N	Y	N	Y	Y	N	Y	Y	Y	Y	Y	Y	Y	Y

^aHydrogen bonds made between the ALDH monomers and trimers were calculated and recorded. Specific interactions between the monomer–monomer interface (αG:αG, β18:β19) and the dimer–dimer interface (β5:β5) were compared between the different assemblies. If a specific residue made a H-bond interaction between the correct secondary structure interface (either on the monomer or the trimer), then it is counted as present (P). The identity of the amino acid residue in ALDH2 is listed and whether it is conserved between ALDH2 and ALDH1B1 (Y) or not (N). Total H-bond interactions by subunit are also recorded (interaction cutoff of 3.5 Å) by subunit. The monomer is designated the A subunit, its dimer is designated the B subunit, the subunit opposite A in the dimer–dimer interface that participates in β5:β5 interactions is the D subunit, and the diagonal subunit which participates in no canonical interactions is the C subunit.