The minimum sequence of the enzymatic (A) subunit of Shiga toxin (STX) required for activity was investigated by introducing N-terminal and C-terminal deletions in the molecule. Enzymatic activity was assessed by using an in vitro translation system. A 253-amino-acid STX A polypeptide, which is recognized as the enzymatically active portion of the 293-amino-acid A subunit, expressed less than wild-type levels of activity. In addition, alteration of the proposed nicking site between Ala-253 and Ser-254 by site-directed mutagenesis apparently prevented proteolytic processing but had no effect on the enzymatic activity of the molecule. Therefore, deletion analysis was used to identify amino acid residue 271 as the C terminus of the enzymatically active portion of the STX A subunit. STX A polypeptides with N-terminal and C-terminal deletions were released into the periplasmic space of Escherichia coli by fusion to the signal peptide and the first 22 amino acids of Shiga-like toxin type II, a member of the STX family. Although these fusion proteins expressed less than wild-type levels of enzymatic activity, they confirmed the previous finding that Tyr-77 is an active-site residue. Therefore, the minimum domain of the A polypeptide which was required for the expression of enzymatic activity was defined as StxA residues 75 to 268.

To determine the HIV-1 genetic diversity in Yemen, 19 strains collected from men and women were sequenced in pol and six of those were full genome sequenced; all were phylogenetically analyzed. Using the pol sequence data, nine (47.3%) were subtype B, six (31.6%) subtype C, two (10.5%) subtype D, one strain (5.3%) subtype A, and another (5.3%) a unique recombinant form (URF). Concordant phylogenies were also obtained for the six strains full genome sequenced. Most of the strains were from the capitol, Sana'a (n=16). Five of the C strains clustered with African Cs, and one clustered with the Indian C strains. Of the two subtype D strains, one clustered with Ugandan strains and one with Cameroon. The subtype A strain was similar to a Cameroon variant of subtype A and the URF strain was a recombinant between CRF11, CRF13, and subtype B. The HIV epidemic in Yemen is extremely complex, with strains of HIV-1 that have originated in East and West Africa, Europe, and India.

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Shiga toxin (STX) is a ribosome-inactivating cytotoxin produced by Shigella dysenteriae serotype 1. The enzymatic domain of the STX A polypeptide has been defined by introducing amino- and carboxy-terminal deletions in the polypeptide and assessing activity in a cell-free translation system. Three recombinant forms of StxA which possess enzymatic activity were genetically fused to a 165-amino-acid polypeptide derived from CD4, the cellular receptor for human immunodeficiency virus type 1 (HIV-1). This strategy eliminated the STX receptor-binding subunit and directed the hybrid toxins to cells expressing the HIV-1 surface glycoprotein gp120. A bacterial lysate containing these toxin chimeras killed the HIV-1-infected T-cell line 8E5 but was not cytotoxic toward the uninfected parental cell line A3.01. This cytotoxic activity was specifically inhibited by monoclonal antibodies which block the interaction between CD4 and gp120. These StxA-CD4 hybrids add to the repertoire of recombinant fusion proteins which possess the capacity to selectively kill HIV-1-infected T cells.

Even though attempts have been effectively applied to eradicate the neonatal tetanus through widespread childhood vaccination and improved conditions at delivery, it remains major cause of infant mortality and continues a problem of public health in developing countries including Yemen.  The aims of this study were to determine the tetanus immunization status, the association between the risk factors and failure of protection in pregnant women at time of delivery. This cross-sectional study included 476 women seeking care for delivery at Al Thawra Modern General Hospital and Al Sabain Hospital, women age ranged from 16-49 years old. Immunization information and factors affecting it were obtained through a standard questionnaire. Serum samples were collected and level of IgG antibody against Clostridium tetani was measured by ELISA technique. Protected women were defined as those with serum antibody levels > or = 0.6 IU/ml.  The total vaccine covering rate of tetanus was 87%, and  maternal vaccine rate was 33.6%, the protective rate at time of delivery was 68.5%. There were significant association between  unvaccinated (OR=18.6), older ages (OR=1.7), rural residency (OR=34) and malaria infection during pregnancy (OR=2.9); with protection failure in pregnant women at time of delivery. It can be concluded that the total vaccine coverage rate and antenatal tetanus vaccine rate were insufficient. In addition, the protective rate at time of delivery was low and large numbers of neonate are susceptible to neonatal tetanus and death. Vaccinating every pregnant woman with at least one dose of TT would be an affordable and effective way to protect against neonatal tetanus, and would be a step toward eliminating the deaths that continue to occur due to this preventable disease in Yemen.