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Arabidopsis Toc33 (atToc33) is a GTPase and a member of the Toc (translocon at the outer-envelope membrane of chloroplasts) complex that associates with precursor proteins during protein import into chloroplasts. By inference from the crystal structure of psToc34, a homologue in pea, the arginine at residue 130 (Arg 130 ) has been implicated in the formation of the atToc33 dimer and in intermolecular GTPase activation within the dimer. Here we report the crystal structure at 3.2-Å resolution of an atToc33 mutant, atToc33(R130A), in which Arg 130 was mutated to alanine. Both in solution and in crystals, atToc33(R130A) was present in its monomeric form. In contrast, both wild-type atToc33 and another pea Toc GTPase homologue, pea Toc159 (psToc159), were able to form dimers in solution. Dimeric atToc33 and psToc159 had significantly higher GTPase activity than monomeric atToc33, psToc159, and atToc33(R130A). Molecular modeling using the structures of psToc34 and atToc33(R130A) suggests that, in an architectural dimer of atToc33, Arg 130 from one monomer interacts with the ␤-phosphate of GDP and several other amino acids of the other monomer. These results indicate that Arg 130 is critical for dimer formation, which is itself important for GTPase activity. Activation of GTPase activity by dimer formation is likely to be a critical regulatory step in protein import into chloroplasts.Chloroplast biogenesis relies on the import from the cytosol of the majority of chloroplast proteins, which are synthesized as precursors with N-terminal targeting signals. Import of precursor proteins into chloroplasts is mediated by a protein translocon complex, which is composed of the Toc 2 (translocon at the outer envelope membrane of chloroplasts) and the Tic (translocon at the inner envelope membrane of chloroplasts) proteins (for reviews, see Refs. 1 and 2). Three Toc proteins, Toc159, Toc75, and Toc34, form the core of the Toc complex (3). In Arabidopsis, Toc34 is encoded by two genes, atToc33 and atToc34, which share 59 and 64% amino acid identity with pea Toc34 (psToc34), respectively (4, 5). atToc33 is the major functional form in leaf chloroplasts (6, 7).Toc75 forms a protein-conducting channel across the outer membrane (8, 9). Toc34 has a cytosol-exposed GTPase domain followed by a C-terminal membrane anchor (10). Toc159 consists of an acidic N-terminal domain, followed by a GTPase domain homologous to that of Toc34, and a membrane-protected C-terminal domain (11). Toc159 and Toc34 function as the initial receptors for incoming precursor molecules. Nonhydrolyzable GTP analogues severely inhibit precursor binding to chloroplasts (12, 13). It has also been shown in vitro that the sequential transfer of precursors between these two receptors is regulated by GTP hydrolysis (14). Targeting of the two receptors themselves to chloroplasts is also dependent on GTP (15-19). Therefore activation and regulation of the GTPase activity of these two receptors are critical for protein import into chloroplasts.Previously we have reported th...

COVID-19 is an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In Sudan, several hematological studies were conducted to study the ABO blood group distribution among the population, in which the "O" blood group was dominating followed by the "A" blood group. However, there is no systematic study that has been done to correlate between COVID-19 infection and the population’s blood group types, therefore we have intended to study the possible effect of blood group on the acquisition of COVID-19 infection. A questionnaire-based case-control study was carried out on 557 COVID-19 patients in Sudan, factors such as age, blood group, previous malaria infection, back history ailments such as diabetes, hypertension, and symptoms suffered were also considered and analyzed. The number of infected females was more than males, whereas the age between 25 to 35 years was the most affected age group. O Rh-positive (O+) blood group was the least affected by the disease while “A” Rh-negative (A-) individuals were the most venerable. Symptoms like fatigue, fever, and loss of smelling sensation were the major ones among the patients. Whereas 13% of SARS-COV-2 positive individuals remained asymptomatic. Since the Sudan population is largely constituted of “O” Rh-positive inhabitants (approx. 50%) these results might explain the relatively lower COVID-19 incidence in the country.

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