Plasmodium berghei and Plasmodium chabaudi are widely used model malaria species. Comparison of their genomes, integrated with proteomic and microarray data, with the genomes of Plasmodium falciparum and Plasmodium yoelii revealed a conserved core of 4500 Plasmodium genes in the central regions of the 14 chromosomes and highlighted genes evolving rapidly because of stage-specific selective pressures. Four strategies for gene expression are apparent during the parasites' life cycle: (i) housekeeping; (ii) host-related; (iii) strategy-specific related to invasion, asexual replication, and sexual development; and (iv) stage-specific. We observed posttranscriptional gene silencing through translational repression of messenger RNA during sexual development, and a 47-base 3′ untranslated region motif is implicated in this process.

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Onychophora are ancient, carnivorous soft-bodied invertebrates which capture their prey in slime that originates from dedicated glands located on either side of the head. While the biochemical composition of the slime is known, its unusual nature and the mechanism of ensnaring thread formation have remained elusive. We have examined gene expression in the slime gland from an Australian onychophoran, Euperipatoides rowelli, and matched expressed sequence tags to separated proteins from the slime. The analysis revealed three categories of protein present: unique high-molecular-weight proline-rich proteins, and smaller concentrations of lectins and small peptides, the latter two likely to act as protease inhibitors and antimicrobial agents. The predominant proline-rich proteins (200 kDaþ) are composed of tandem repeated motifs and distinguished by an unusually high proline and charged residue content. Unlike the highly structured proteins such as silks used for prey capture by spiders and insects, these proteins lack ordered secondary structure over their entire length. We propose that on expulsion of slime from the gland onto prey, evaporative water loss triggers a glass transition change in the protein solution, resulting in adhesive and enmeshing thread formation, assisted by cross-linking of complementary charged and hydrophobic regions of the protein. Euperipatoides rowelli has developed an entirely new method of capturing prey by harnessing disordered proteins rather than structured, silk-like proteins.

The pupal cocoon of the domesticated silk moth Bombyx mori is the best known and most extensively studied insect silk. It is not widely known that Apis mellifera larvae also produce silk. We have used a combination of genomic and proteomic techniques to identify four honey bee fiber genes (AmelFibroin1–4) and two silk-associated genes (AmelSA1 and 2). The four fiber genes are small, comprise a single exon each, and are clustered on a short genomic region where the open reading frames are GC-rich amid low GC intergenic regions. The genes encode similar proteins that are highly helical and predicted to form unusually tight coiled coils. Despite the similarity in size, structure, and composition of the encoded proteins, the genes have low primary sequence identity. We propose that the four fiber genes have arisen from gene duplication events but have subsequently diverged significantly. The silk-associated genes encode proteins likely to act as a glue (AmelSA1) and involved in silk processing (AmelSA2). Although the silks of honey bees and silkmoths both originate in larval labial glands, the silk proteins are completely different in their primary, secondary, and tertiary structures as well as the genomic arrangement of the genes encoding them. This implies independent evolutionary origins for these functionally related proteins.

SummaryMalaria parasites suffer severe losses in the mosquito as they cross the midgut, haemolymph and salivary gland tissues, in part caused by immune responses of the insect. The parasite compensates for these losses by multiplying during the oocyst stage to form the infectious sporozoites. Upon human infection, malaria parasites are again attenuated by sustained immune attack. Here, we report a single copy gene that is highly conserved amongst Plasmodium species that encodes a secreted protein named PxSR . The predicted protein is composed of a unique combination of metazoan protein domains that have been previously associated with immune recognition/ activation and lipid/protein adhesion interactions at the cell surface, namely: (i) scavenger receptor cysteine rich (SRCR); (ii) pentraxin (PTX); (iii) polycystine-1, lipoxygenase, alpha toxin (LH2/PLAT); (iv) Limulus clotting factor C, Coch-5b2 and Lgl1 (LCCL). In our assessment the PxSR molecule is completely novel in biology and is only found in Apicomplexa parasites. We show that PxSR is expressed in sporozoites of both human and rodent malaria species. Disruption of the PbSR gene in the rodent malaria parasite P. berghei results in parasites that form normal numbers of oocysts, but fail to produce any sporozoites. We suggest that, in addition to a role in sporogonic development, PxSR may have a multiplicity of functions.

Silks are strong protein fibers produced by a broad array of spiders and insects. The vast majority of known silks are large, repetitive proteins assembled into extended beta-sheet structures. Honeybees, however, have found a radically different evolutionary solution to the need for a building material. The 4 fibrous proteins of honeybee silk are small ( approximately 30 kDa each) and nonrepetitive and adopt a coiled coil structure. We examined silks from the 3 superfamilies of the Aculeata (Hymenoptera: Apocrita) by infrared spectroscopy and found coiled coil structure in bees (Apoidea) and in ants (Vespoidea) but not in parasitic wasps of the Chrysidoidea. We subsequently identified and sequenced the silk genes of bumblebees, bulldog ants, and weaver ants and compared these with honeybee silk genes. Each species produced orthologues of the 4 small fibroin proteins identified in honeybee silk. Each fibroin contained a continuous predicted coiled coil region of around 210 residues, flanked by 23-160 residue length N- and C-termini. The cores of the coiled coils were unusually rich in alanine. There was extensive sequence divergence among the bee and ant silk genes (<50% similarity between the alignable regions of bee and ant sequences), consistent with constant and equivalent divergence since the bee/ant split (estimated to be 155 Myr). Despite a high background level of sequence diversity, we have identified conserved design elements that we propose are essential to the assembly and function of coiled coil silks.

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