Structural basis for Na(+) transport mechanism by a light-driven Na(+) pump.

Krokinobacter eikastus rhodopsin 2 (KR2) is the first light-driven Na(+) pump discovered, and is viewed as a potential next-generation optogenetics tool. Since the positively charged Schiff base proton, located within the ion-conducting pathway of all light-driven ion pumps, was thought to prohibit the transport of a non-proton cation, the discovery of KR2 raised the question of how it achieves Na(+) transport. Here we present crystal structures of KR2 under neutral and acidic conditions, which represent the resting and M-like intermediate states, respectively. Structural and spectroscopic analyses revealed the gating mechanism, whereby the flipping of Asp116 sequesters the Schiff base proton from the conducting pathway to facilitate Na(+) transport. Together with the structure-based engineering of the first light-driven K(+) pumps, electrophysiological assays in mammalian neurons and behavioural assays in a nematode, our studies reveal the molecular basis for light-driven non-proton cation pumps and thus provide a framework that may advance the development of next-generation optogenetics.

The regulatory mechanism of ion permeation through a channelrhodopsin derived from Mesostigma viride (MvChR1).

The five glutamate (E) residues of transmembrane (TM)-2 of channelrhodopsin (CrChR)-2 are conserved among several members of the ChR family. A point mutation of one of them, E97, to a nonpolar alanine (E97A) reduced the photocurrent amplitude without influencing other photocurrent properties. The charge at this position is also the determinant of the Gd(3+)-dependent block of the channel. It has thus been suggested that E97 interacts with hydrated cations to facilitate their permeation and that these residues are the primary binding sites of Gd(3+). However, the counterpart of this position is alanine for MvChR1 from Mesostigma viride. Here we investigated the ion permeation and the Gd(3+)-dependent channel block of MvChR1. We found that the high-affinity binding site of Gd(3+) was absent in MvChR1, but was dependent on the negativity at this position. However, the ion permeation through the channel was markedly interfered with a negative charge at this position. Based on these findings, it is proposed that the ions can pass through the pore with minimal interaction with this position.

Cervical cancer in low-income countries: A Bangladeshi perspective.

Cervical cancer is the fourth most common cancer among women worldwide, with approximately 70% of cases involving infection with human papillomavirus (HPV) genotypes 16 and 18. According to International Agency for Research on Cancer, more than 50 million Bangladeshi women are at risk of developing cervical cancer, and 17 686 new cases and 10 362 deaths occur annually. If diagnosed at the precursor stage, however, cervical cancer is a condition that can be successfully treated. As a result, screening programs are necessary to identify the disease before it progresses to invasive cancer. In the present review, we discuss the overall situation of cervical cancer in Bangladesh, summarizing the sociodemographic status of affected women, associated risk factors, screening approaches, and treatment options. We emphasize the potential of visual inspection with acetic acid (VIA) as a cost-effective screening approach for detecting cervical lesions among poor women in the community. In a resource-limited country such as Bangladesh, VIA may represent an ideal model to build an effective awareness campaign through urban and rural hospitals, community-based clinics, and other health facilities available in industry.

Epidemiology, clinical features, and impact of food habits on the risk of hepatocellular carcinoma: A case-control study in Bangladesh.

Hepatocellular carcinoma (HCC) is the sixth most common cancer and the third most common cause of cancer mortality worldwide. Infection with hepatitis B virus (HBV) and/or hepatitis C virus (HCV) is the most predominant cause of HCC. Concerns arise for the presence of additional risk factors, as there is still a large proportion of patients without HBV or HCV infection. Previous studies have reported that higher intake of fruits and vegetables and reduced consumption of red/processed meat might play a protective role in HCC etiology, though the nationwide proof is limited. Hence, we studied multiple risk factors including food habit, lifestyle, and clinical implications of HCC patients in Bangladeshi. Demographic, clinical, and biochemical data, as well as data on food habits, were collected in this study. Our results indicated that a high intake of rice (AOR 4.28, 95% CI 1.48 to 14.07, p = 0.011), low intake of fruits (AOR = 4.41 95% CI 1.48-15.46; p = 0.012), leafy vegetables (AOR = 2.80, 95% CI 1.32-6.08; p = 0.008), and fish (AOR = 4.64 95% CI 2.18-10.23; p<0.001) increased the HCC risk. Moreover, a high intake of eggs (AOR = 2.07 95% CI 0.98-4.43; p = 0.058) also showed an increased risk. Roti, non-leafy vegetables, red meat, and tea were found to have no association with HCC risk. This study revealed that food habit patterns and lifestyle may have a profound effect on HCC development among Bangladeshi patients in addition to well established risk factors.

A Chimera Na+-Pump Rhodopsin as an Effective Optogenetic Silencer.

With the progress of optogenetics, the activities of genetically identified neurons can be optically silenced to determine whether the neurons in question are necessary for the network performance of the behavioral expression. This logical induction is expected to be improved by the application of the Na+ pump rhodopsins (NaRs), which hyperpolarize the membrane potential with negligible influence on the ionic/pH balance. Here, we made several chimeric NaRs between two NaRs, KR2 and IaNaR from Krokinobacter eikastus and Indibacter alkaliphilus, respectively. We found that one of these chimeras, named I1K6NaR, exhibited some improvements in the membrane targeting and photocurrent properties over native NaRs. The I1K6NaR-expressing cortical neurons were stably silenced by green light irradiation for a certain long duration. With its rapid kinetics and voltage dependency, the photoactivation of I1K6NaR would specifically counteract the generation of action potentials with less hyperpolarization of the neuronal membrane potential than KR2.

Near-infrared (NIR) up-conversion optogenetics.

Non-invasive remote control technologies designed to manipulate neural functions have been long-awaited for the comprehensive and quantitative understanding of neuronal network in the brain as well as for the therapy of neurological disorders. Recently, it has become possible for the neuronal activity to be optically manipulated using biological photo-reactive molecules such as channelrhodopsin (ChR)-2. However, ChR2 and its relatives are mostly reactive to visible light, which does not effectively penetrate through biological tissues. In contrast, near-infrared (NIR) light (650-1450 nm) penetrates deep into the tissues because biological systems are almost transparent to light within this so-called 'imaging window'. Here we used lanthanide nanoparticles (LNPs), composed of rare-earth elements, as luminous bodies to activate ChRs since they absorb low-energy NIR light to emit high-energy visible light (up-conversion). Here, we created a new type of optogenetic system which consists of the donor LNPs and the acceptor ChRs. The NIR laser irradiation emitted visible light from LNPs, then induced the photo-reactive responses in the near-by cells that expressed ChRs. However, there remains room for large improvements in the energy efficiency of the LNP-ChR system.