A. Charbit et al., A ROLE FOR RESIDUE-151 OF LAMB IN BACTERIOPHAGE-LAMBDA ADSORPTION - POSSIBLE STERIC EFFECT OF AMINO-ACID SUBSTITUTIONS, Journal of bacteriology, 176(11), 1994, pp. 3204-3209
LamB is the cell surface receptor for bacteriophage lambda. LamB misse
nse mutations yielding resistance to h have been previously grouped in
two classes. Class I mutants block growth of lambda with mild-type ho
st range (lambda h(+)) but support growth of one-step extended-host-ra
nge mutants (lambda h). Class II mutants block lambda h but support gr
owth of two-step extended host range mutants (lambda hh). While Class
I mutations occur at 11 different amino acid sites, in five distinct
portions of LamB, all the Class II mutations analyzed previously corre
spond to the same G-to-D change at amino acid 151. We generated by in
vitro mutagenesis four different new substitutions at site 151 (to S,
V, R, and C). Two of the mutants (G-151 --> V [G151V] and G151R) were
of Class II, while the two others (G151S and G151C) were of Class I, d
emonstrating that not only the site but also the nature of the substit
utions at residue 151 was critical for the phage sensitivity phenotype
s. The introduction of a negatively charged, a positively charged, or
an aliphatic nonpolar residue at site 151 of LamB prevented both lambd
a h(+) and lambda h adsorption, indicating that the block is not due t
o a charge effect. In contrast to G151D, which was sensitive to all th
e lambda hh phages, G151V and G151R conferred sensitivity to only fou
r Of the five lambda hh phages. Thus, G151V and G151R represent a new
subclass of Class II LamB mutations that is more restrictive with res
pect to the growth of lambda hh. Our results agree with the hypothesi
s that residue 151 belongs to an accessibility gate controlling the ac
cess to the phage tight-binding site and that substitutions at this re
sidue affect the access of the phage to the binding site in relation t
o the size of the substitute side chain (surface area): the most restr
ictive changes are G151V and G151R, followed to a lesser extent by G15
1D and then by G151S and G151C.