posted on 2024-01-09, 17:09authored byJiming Chen, Tanner J. Dean, Diwakar Shukla
The
parasitic plant witchweed, Striga hermonthica, results in agricultural losses of billions of dollars per year.
It perceives its host via plant hormones called strigolactones, which
act as germination stimulants for witchweed. Strigolactone signaling
involves substrate binding to the strigolactone receptor, followed
by substrate hydrolysis and a conformational change from an inactive,
or open state, to an active, or closed state. In the active state,
the receptor associates with a signaling partner, MAX2. Recently,
it was shown that this MAX2 association process acts as a strong contributor
to the uniquely high signaling activity observed in ShHTL7; however, it is unknown why ShHTL7 has enhanced
MAX2 association affinity. Using an umbrella sampling molecular dynamics
approach, we characterized the association processes of AtD14, ShHTL7, a mutant of ShHTL7,
and ShHTL6 with MAX2 homologue OsD3. From these results, we show that ShHTL7 has
an enhanced standard binding free energy of OsD3
compared to those of the other receptors. Additionally, our results
suggest that the overall topology of the T2/T3 helix region is likely
an important modulator of MAX2 binding. Thus, differences in MAX2
association, modulated by differences in the T2/T3 helix region, are
a contributor to differences in signaling activity between different
strigolactone receptors.