PURPOSE-Pathogenic variants in GJB2 are the most common cause of autosomal recessive sensorineural hearing loss. The classification of c.101T>C/p.Met34Thr and c.109G>A/p.Val37Ile in GJB2 are controversial. Therefore, an expert consensus is required for the interpretation of these two variants. METHODS-The ClinGen Hearing Loss Expert Panel collected published data and shared unpublished information from contributing laboratories and clinics regarding the two variants. Shen et al.

Increased conformational flexibility is the prevailing explanation for the high catalytic efficiency of cold-adapted enzymes at low temperatures. However, less is known about the structural determinants of flexibility. We reported two novel cold-adapted zinc metalloproteases in the thermolysin family, vibriolysin MCP-02 from a deep sea bacterium and vibriolysin E495 from an Arctic sea ice bacterium, and compared them with their mesophilic homolog, pseudolysin from a terrestrial bacterium. Their catalytic efficiencies, k cat /K m (10 -40°C), followed the order pseudolysin < MCP-02 < E495 with a ratio of ϳ1:2:4. MCP-02 and E495 have the same optimal temperature (T opt , 57°C, 5°C lower than pseudolysin) and apparent melting temperature (T m ‫؍‬ 64°C, ϳ10°C lower than pseudolysin). Structural analysis showed that the slightly lower stabilities resulted from a decrease in the number of salt bridges. Fluorescence quenching experiments and molecular dynamics simulations showed that the flexibilities of the proteins were pseudolysin < MCP-02 < E495, suggesting that optimization of flexibility is a strategy for cold adaptation. Molecular dynamics results showed that the ordinal increase in flexibility from pseudolysin to MCP-02 and E495, especially the increase from MCP-02 to E495, mainly resulted from the decrease of hydrogen-bond stability in the dynamic structure, which was due to the increase in asparagine, serine, and threonine residues. Finally, a model for the cold adaptation of MCP-02 and E495 was proposed. This is the first report of the optimization of hydrogen-bonding dynamics as a strategy for cold adaptation and provides new insights into the structural basis underlying conformational flexibility.Cold-adapted enzymes, produced by organisms thriving in permanently cold habitats (deep sea, polar regions, and alpine regions), are characterized by high catalytic efficiencies at low temperatures and low stabilities at high temperatures (1-4). Different enzymes may adopt different strategies for cold adaptation, e.g. optimization of flexibility (2, 5) and optimization of electrostatic potential (6 -8). The prevailing hypothesis is that cold-adapted enzymes obtain high catalytic efficiencies by increasing conformational flexibility at the expense of stability (4, 9). The comparison of crystal structures has revealed some structural features that might be related to the cold adaptation of enzymes, including more non-branching or small residues, more asparagines, less arginines, more negative net charges, larger hydrophobic accessible surfaces, less salt bridges, and longer loops (3, 10). However, less is currently known about how the conformational flexibility is determined by these features, because no structural feature is present in all coldadapted enzymes, and no structural features consistently correlate with cold adaptation (3). Moreover, there are also reports about cold-adapted enzymes that possess both high activities and high stabilities (11)(12)(13). Laboratory evolution studies also show that high catal...

Fjords and open oceans are two typical marine ecosystems in the Arctic region, where glacial meltwater and sea ice meltwater have great effects on the bacterioplankton community structure during the summer season. This study aimed to determine the differences in bacterioplankton communities between these two ecosystems in the Arctic region. We conducted a detailed census of microbial communities in Kongsfjorden (Spitsbergen) and the Chukchi Borderland using high-throughput pyrosequencing of the 16S rRNA gene. Gammaproteobacteria and Bacteroidetes were the dominant members of the bacterioplankton community in Kongsfjorden. By contrast, the most abundant bacterial groups in the surface seawater samples from the Chukchi Borderland were Alphaproteobacteria and Actinobacteria. Differences in bacterial communities were found between the surface and subsurface waters in the investigation area of the Chukchi Borderland, and significant differences in bacterial community structure were also observed in the subsurface water between the shelf and deep basin areas. These results suggest the effect of hydrogeographic conditions on bacterial communities. Ubiquitous phylotypes found in all the investigated samples belonged to a few bacterial groups that dominate marine bacterioplankton communities. The sequence data suggested that changes in environmental conditions result in abundant rare phylotypes and reduced amounts of other phylotypes.

In order to assess bacterial diversity within four surface sediment samples (0-5 cm) collected from the Pacific Arctic Ocean, 16S ribosomal DNA clone library analysis was performed. Near full length 16S rDNA sequences were obtained for 463 clones from four libraries and 13 distinct major lineages of Bacteria were identified (alpha, beta, gamma, delta and epsilon-Proteobacteria, Acidobacteria, Bacteroidetes, Chloroflexi, Actinobacteria, Firmicutes, Planctomycetes, Spirochetes, and Verrucomicrobia). alpha, gamma, and delta-Proteobacteria, Acidobacteria, Bacteroidetes, Actinobacteria were common phylogenetic groups from all the sediments. The gamma-Proteobacteria were the dominant bacterial lineage, representing near or over 50% of the clones. Over 35% of gamma-Proteobacteria clones of four clone library were closely related to cultured bacterial isolates with similarity values ranging from 94 to 100%. The community composition was different among sampling sites, which potentially was related to geochemical differences.