THE LUX AUTOINDUCER-RECEPTOR INTERACTION IN VIBRIO-HARVEYI - BINDING PARAMETERS AND STRUCTURAL REQUIREMENTS FOR THE AUTOINDUCER

To assess the binding parameters and the structure-function relationsh ip of the Vibrio harveyi lux autoinducer, N-(D-3-hydroxybutanoyl)homos erine lactone (D-HBHL), to light emission, a series of acylhomoserine lactone analogues were synthesized and their effects on the stimulatio n of luminescence of an autoinducer-deficient mutant of V. harveyi, D1 , examined. Of the analogues with 3-hydroxyacyl chains, only N-(3-hydr oxyvaleryl)homoserine lactone (HVHL) could act as an inducer, with abo ut 85% of the potency of D-HBHL in stimulation of luminescence; the ap parent K-d of the putative receptor for HVHL was 3.8 mu M, close to th at for the natural autoinducer (1.4 mu M). Analogues with longer 3-hyd roxyacyl chains, N-(3-hydroxyhexanoyl)homoserine lactone and N-(3-hydr oxyheptanoyl)homoserine lactone, acted as competitive inhibitors of HB HL with apparent K-I values of 77 and 53 mu M respectively. Replacemen t of the 3-hydroxybutanoyl moiety with a 3-methylbutanoyl or 3-methoxy butanoyl group created weak competitive inhibitors, N-(isovaleryl)- an d N-(3-methoxybutanoyl)- homoserine lactones, with apparent K-I values of 150 and 360 mu M respectively. Two other analogues, N-(2-hydroxybu tanoyl)- and N-(4-hydroxybutanoyl)-homoserine lactone, could neither s timulate nor inhibit luminescence. The approach used in these studies to demonstrate binding of autoinducer analogues at the same site, as w ell as measurement of the relative dissociation constant, may be of va lue in analysing analogues activating or inhibiting luminescence and o ther processes that are under control of acylhomoserine lactone autore gulators.