e-based transmission blocking vaccines for malaria in a well-validated, robust, and inexpensive host expression platform. Chimeric genes in which the coding sequence of the Grl1p proprotein was placed downstream of the coding regions of either Pfs25, or the 10C fragment of Pfs48/45 (herein referred to as Pfs48/45^10C^) were prepared. The 10C fragment was chosen based on a previous report of its increased stability in *E. coli* relative to full length Pfs48/45 protein \[[@bib11]\]. Gene fragments were codon-harmonized according to Kumar et al. \[[@bib12],[@bib23]\], and fusion constructs were expressed in the SHuffle strain of *E. coli* \[[@bib42]\]) engineered for improved production of disulfide-bonded proteins in the cytoplasm.

Consistent with previous findings \[[@bib12],[@bib19],[@bib23]\] both Pfs25 and Pfs48/45^10C^ were largely insoluble when expressed in *E. coli* at 30 °C, although very small amounts of Pfs25 remained soluble after induction at 16 °C. By contrast, significant amounts of Pfs25:Grl1p and Pfs48/45^10C^:Grl1p fusion proteins produced at 30 °C were detected in filtered extracts indicating that Grl1p conferred improved solubility to each of the antigens. In the case of the Pfs25:Grl1p fusion, approximately 180-fold more soluble protein was recovered compared with Pfs25 alone when both were induced at 16 °C (13.5 mg versus 0.075 mg per liter, respectively, see [Table 4](#tbl4){ref-type="table"}). Although similar comparisons of fold increase were not possible for Pfs48/45^10C^ and Pfs48/45^10C^:Grl1p due to the lack of recovery of any quantifiable amounts of soluble Pfs48/45^10C^, similar amounts of soluble Pfs48/45^10C^:Grl1p were easily obtained per liter of non-optimized culture (A. Agrawal, unpublished results).Table 1Average DLS volume distribution measurements of G-SOME particles.Table 1G-SOME proteinPeak diameter by volumePercent by volumePfs2510100Pfs25:Grl1p384010660Pfs48/45^10C^:Grl1p25507050Grl1p13100Table 2**Pfs25, Pfs25:Grl1p, Pfs48/45**^**10C**^**Grl1p, and Grl1p 