As-p18 is a developmentally regulated fatty-acid-binding protein that is one of the most abundant components of the perivitelline fluid surrounding the developing larval stages of the parasitic nematode Ascaris suum
(Mei et al.
). The infective third-stage (L3) larva undergoes developmental arrest until ingestion by the host and may survive for up to seven years in the egg before infection of the host, but little is known of the biochemical and physiological basis of such long-term survival. As-p18 displays sequence similarity to the mammalian group of intracellular fatty-acid-binding proteins (iFABPs), but modelling indicated that there may be differences in its ligand-binding site and the existence of extended loops exposed on the surface of the expected ten-stranded β-barrel (Mei et al.
). These differences could relate to ligand specificity and interaction with as yet uncharacterized protein or membrane interaction partners. Phylogenetic analysis reveals that As-p18, together with other potential homologues and paralogues in Caenorhabditis elegans
, comprise a distinct protein class (‘nemFABPs’) within the FABP family that is unique to nematodes (Plenefisch et al.
). The presence of a leader peptide in mRNAs encoding As-p18 and direct evidence of its secretion from the synthesizing cell further distinguish this protein, and possibly nemFABPs in general, from FABPs found in other animal groups. The atypical features of As-p18s may reflect adaptation to a specific function within the egg related to the survival of nematode larvae in general, including those of the highly pathogenic agents of filariasis in humans (Kennedy & Harnett, 2001
; Michalski et al.
Here, we report crystallization conditions for As-p18 and the utility of microfocus beamlines to analyse its structure. Whilst the crystals showed no obvious signs of disorder under optical microscopy, it became apparent from initial X-ray diffraction observations that the crystals were composed of multiple microdomains. This prevented data collection on a conventional beamline because the diffraction patterns revealed the presence of multiple lattices. Only when the crystals were brought to a microfocus beamline could a complete data set be collected. The data-collection strategy and data processing is presented here.