Functional analyses reveal an important role for tyrosine residues in the staphylococcal multidrug efflux protein QacA

Table 1 Phenotypic profiles of QacA tyrosine mutants

QacA mutation	QacA expression (% wt QacA)^c	minimum inhibitory concentration (μg ml^-1)^a.b
		monovalent substrates			bivalent substrates
		dyes		Qacs^d		Bg	Di
		Et	PyY	Bc	Dc	Ch	Dd
wt QacA	100	1200	500	50	350	12	300
vector	N/A	400	50	30	100	2	100
Y63V	86	200	50	30	150	4	100
Y63F	50	1400	400	50	250	12	300
Y315A	64	800	500	50	300	12	400
Y315F	75	1000	500	50	300	12	300
Y358S	80	600	400	50	100	8	200
Y358F	34	1400	400	50	300	16	300
Y366A	106	1200	300	50	100	12	300
Y366V	50	1200	400	50	300	12	300
Y366F	99	800	500	50	300	12	400
Y410A	132	400	50	45	100	3	100
Y410V	67	200	50	30	100	7	300
Y410F	58	200	100	50	250	12	300
Y429S	57	200	200	30	250	4	100
Y429F	32	1400	500	60	300	14	400
Y501V	36	800	500	50	300	12	300
Y501F	47	1200	500	50	350	12	400

^a MIC values were determined in E. coli BHB2600 cells expressing wild-type QacA or a mutant derivative and represent the lowest concentration of substrate required to fully inhibit bacterial growth.
^b MIC experiments were conducted in at least triplicate and the median value is presented.
^c QacA protein expression levels are the average of two repeat experiments.
^d Abbreviations: Qacs, quaternary ammonium compounds; Bg, biguanidines; Di, diamidines; Et, ethidium; PyY, pyronin Y; Bc, benzalkonium; Dc, dequalinium; Ch, chlorhexidine; Dd, diamidinodiphenylamine.

ISSN: 1471-2180