Biology subjects

Hassan, A. H.

Publications and source records attributed to Hassan, A. H..

4 recordsLinked to original sources

bioRxiv2026

Mechanistic insights into E. coli recovery from growth arrest

Bacteria survive hostile conditions in clinically relevant conditions by shutting down protein synthesis, but how they restart growth remains poorly understood. Here, we use an E. coli {Delta}rimM strain, which exhibits a prolonged growth arrest, as a model to investigate how bacteria recover from this arrested state and restore protein synthesis. RimM is a conserved ribosome maturation factor for the 3-major (head) domain of the 16S rRNA within the bacterial 30S subunit. The loss of RimM causes a significantly longer delay in recovery than other 30S maturation factors, including RbfA - the presumed primary factor in 30S maturation. Cryo-EM analysis of {Delta}rimM ribosomes revealed a delayed recruitment of ribosomal proteins to the 30S head domain and increased occupancy of the initiation factors IF1 and IF3, as well as recruitment of the silencing factor RsfS to the 50S subunit. These coordinated changes provide a safeguarding mechanism to block the assembly of premature 70S ribosomes. Notably, while the delayed 30S assembly in {Delta}rimM reduces the activity of global protein synthesis during the recovery phase, bacteria attempt to compensate for this deficiency by producing higher levels of the ribosomal machinery, indicating a programmatic change in energy allocation to generate the ribosome machinery. These findings highlight the importance of the RimM-assisted assembly of the ribosomal head domain for bacterial recovery from growth arrest.

molecular biology↗

bioRxiv2026

Phylogenetic based dissection of eukaryotic Mo-insertase functionality: From mechanism to complex assembly

Molybdenum cofactor (Moco) biosynthesis is vitally important for all organisms, yet the domain organization of the eukaryotic molybdenum insertase (Mo-insertase) remains enigmatic. We combine extensive phylogenetic reconstructions, sequence analysis and structural modeling in order to uncover evolutionary and functional principles of eukaryotic Mo-insertases. We note, that the vast majority of plant, fungi and animal species evolved fused E- and G-domains, yet the orientation of both domains in the fusion proteins differs among different eukaryotic lineages. Despite the divergent domain arrangements amongst eukaryotic Mo-insertases the E-domain active site is well conserved, with very few tolerated substitutions in >1,000 sequences. Among the Mo-insertases from different eukaryotic species, vertebrate gephyrin is the only Mo-insertase with a dual function as - next to its metabolic function - it scaffolds inhibitory neurotransmitter receptors in the post synapsis. Gephyrin is surprisingly high conserved, including surface patches not directly involved in catalysis and receptor clustering. This profile suggests additional, as yet uncharacterized, functional constraints on gephyrins evolution. Together, our results reveal how eukaryotic Mo-insertases combine evolutionary domain organization plasticity with stringent active site conservation and recognize the evolutionary constraint on gephyri[n]s surface conservation to be extreme, likely due to its mutual metabolic and neuronal function.

bioinformatics↗

bioRxiv2021

Histopathological Changes In The Intestine Of Infected Pigeons (Columba Livia Domestica) Caused By Helminthes Infection From Al-Qassim, Saudi Arabia

Helminthes infection causes extensive harm to the pigeon host. The purpose of this study was to observe histopathological changes caused by helminths infection. Thirty-five pigeons (C.L. domestica) were purchased weekly from a birds market from Al-Qassim region, Saudi Arabia. Out of the 35 pigeons examined, 9 pigeons (25.71%) were found infected with helminth parasites, which were identified as one cestode (Raillietina sp.), and one nematode (Ascaridia columbae). The infected pigeons suffered from growth retardation, emaciation, weakness, droopiness, and diarrhea. A lot of histopathological changes were seen in the intestine of infected pigeons including atrophy and distortion of villi, infiltration of inflammatory lymphocytic cells, erosion, and loss of the typical structure of the intestine, necrosis in villi, and blood vessels congestion. This study concludes, for the first time in AL-Qassim region-Saudi Arabia, that the infection with helminth parasites caused significant histopathological changes in the intestines of the infected pigeons, and this could lead to increased mortality to the infected pigeons. Further work is necessary in Saudi Arabia to determine the prevalence and biological factors that have a significant impact on the helminth parasites community.

zoology↗

bioRxiv2018

Protective effects of low-intensity pulsed ultrasound on mandibular condylar cartilage exposed to mechanical overloading

The aim of this study was to examine the role of low-intensity pulsed ultrasound (LIPUS) exposure in the onset and early progression of temporomandibular joint (TMJ) osteoarthritis (TMJ-OA) induced by mechanical overloading. Fifteen-week-old male Wistar rats were divided into two experimental groups and a control group (n = 5 each). In the experimental groups, both TMJs were subjected to mechanical overloading by forced mouth opening using a jaw-opening device for 3 h/day for 5 continuous days. After mechanical overloading, TMJs in one experimental group were exposed to LIPUS for 20 min/day. After the experiments, mandibles were resected from the rats, and the condyles were processed. The bones were analyzed using high-resolution microcomputed tomography (micro-CT). The resected TMJs were also subjected to histological analysis and immunohistochemical staining. Micro-CT images of the mandibular condyle showed severe subchondral trabecular bone loss in the experimental group with overloading. Treatment with LIPUS after overloading resulted in decreased subchondral trabecular bone resorption. In TMJ sections from the experimental group with overloading, cell-free regions and proteoglycan loss characterized the cartilage degradation; LIPUS exposure restricted these changes in the mandibular condyle. Furthermore, the number of tartrate-resistant acid phosphatase-positive osteoclasts in the mineralized layer of the condylar cartilage increased after mechanical overloading and decreased after LIPUS treatment. Our findings suggest that LIPUS exposure after mechanical TMJ overloading downregulates subchondral trabecular bone resorption and proteoglycan loss in the mandibular condylar cartilage. Thus, it may prove to be protective effects of LIPUS exposure on onset and early progression of TMJ-OA induced by mechanical overloading.

developmental biology↗