De novo phasing with X-ray laser reveals mosquito larvicide BinAB structure

Abstract

SummaryBinAB is a naturally occurring paracrystalline larvicide distributed worldwide to combat the devastating diseases borne by mosquitoes. These crystals are composed of homologous molecules, BinA and BinB, which play distinct roles in the multi-step intoxication process, transforming from harmless, robust crystals, to soluble protoxin heterodimers, to internalized mature toxin, and finally toxic oligomeric pores. The small size of the crystals, 50 unit cells per edge, on average, has impeded structural characterization by conventional means. Here, we report the structure of BinAB solved de novo by serial-femtosecond crystallography at an X-ray free-electron laser (XFEL). The structure reveals tyrosine and carboxylate-mediated contacts acting as pH switches to release soluble protoxin in the alkaline larval midgut. An enormous heterodimeric interface appears responsible for anchoring BinA to receptor-bound BinB for co-internalization. Remarkably, this interface is largely composed of propeptides, suggesting that proteolytic maturation would trigger dissociation of the heterodimer and progression to pore formation.

Hydroxyethyl cellulose matrix applied to serial crystallography

“…In addition, native sulfur SAD phasing was also achieved 40, 43, 44 . These results indicate that de novo phasing is now routinely available for SFX.…”

Isolation, identification and evaluation of mosquito entomopathogenic Bacillus species and related genera from randomly selected sites in Kenya

“…For example L. sphaericus principle toxin is the Binary toxin (bin) composed of two subunits (binA and binB) located in the chromosome and crystallize together into one parasporal body inform of a toxin dormain and a binding dormain (Berry, 2012;Colletier et al, 2016;Kale et al, 2013). They are also known to produce other less toxic proteins called mosquitocidal toxins (mtx1, 2, 3) expressed during the vegetative stage of the bacterial growth (Berry, 2012).…”

A Bright Future for Serial Femtosecond Crystallography with XFELs

“…Another study reported structure determination of luciferin-regenerating enzyme by single isomorphous replacement with anomalous scattering (SIRAS) using a mercury derivative [23] and requiring 10,000 patterns for each of the native and derivative datasets. Most recently, a novel structure of a mosquito larvicide BinAB has been solved by multiple isomorphous replacement with anomalous scattering (MIRAS) using three different derivatives: mercury, gadolinium and iodine [100]. Another approach successfully used for experimental phasing was based on the use of iodine-containing detergent to purify and crystallize membrane proteins, and serve as a source of anomalous signal for SAD, SIR or SIRAS phase retrieval methods [25].…”