Significant risk and associated factors of active tuberculosis infection in Korean patients with inflammatory bowel disease using anti-TNF agents

AIM:To evaluate the incidence and risk factors of Korean tuberculosis(TB) infection in patients with inflammatory bowel disease(IBD) undergoing anti-TNF treatment.METHODS:The data of IBD patients treated with anti-TNFs in 13 tertiary referral hospitals located in the southeastern region of Korea were collected retrospectively.They failed to show response or were intolerant to conventional treatments,including steroids or immunomodulators.Screening measures for latent TB infection(LTBI)and the incidence and risk factors ofactive TB infection after treatment with anti-TNFs were identified.RESULTS:Overall,376 IBD patients treated with antiTNF agents were recruited(male 255,mean age of anti-TNF therapy 32.5±13.0 years);277 had Crohn’s disease,99 had ulcerative colitis,294 used infliximab,and 82 used adalimumab.Before anti-TNF treatment,screening tests for LTBI including an interferon gamma release assay or a tuberculin skin test were performed in 82.2%of patients.Thirty patients(8%)had LTBI.Sixteen cases of active TB infection including one TB-related mortality occurred during 801 personyears(PY)follow-up(1997.4 cases per 100000 PY)after anti-TNF treatment.LTBI(OR=5.76,95%CI:1.57-21.20,P=0.008)and WBC count<5000 mm3(OR=4.5,95%CI:1.51-13.44,P=0.007)during follow-up were identified as independently associated risk factors.CONCLUSION:Anti-TNFs significantly increase the risk of TB infection in Korean patients with IBD.The considerable burden of TB and marked immunosuppression might be attributed to this risk.

Pancreatic pseudocystocolonic fistula treated without surgical or endoscopic intervention

We report here a case of pancreatic pseudocystocolic fistula that was treated without surgical or endoscopic intervention.A 76-year-old woman,presenting with a fever and epigastric pain,was referred to our institution.Three months prior to this admission,the patient had been admitted to the hospital for acute pancreatitis.Abdominal computerized tomography(CT)revealed a 9 cm pseudocyst containing air,and a fistular opening was observed via colonoscopy.After colonoscopy,the abdominal pain was slightly improved,the fever subsided and laboratory results showed decreased C-reactive protein levels.The observed improvement was likely due to the cleansing of the bowel,which induced spontaneous drainage from the pseudocyst into the colon.Antibiotic therapy was administered and daily bowel cleansing was performed using a polyethylene glycol solution.After three weeks,a follow-up CT revealed that the size of the pseudocyst had decreased significantly from 9 to 5.3 cm.In addition,laboratory tests were improved.The patient was able to resume a normal diet and was discharged in good overall health from the hospital,without aggravation of the symptoms.A colonoscopy performed 3 mo later and a follow-up CT performed 6 mo later confirmed that both the fistula and pseudocyst had completely disappeared.

Translation rate underpins specific targeting of N-terminal transmembrane proteins to mitochondria

Protein biogenesis is a complex process,and complexity is greatly increased in eukaryotic cells through specific targeting of proteins to different organelles.To direct targeting,organellar proteins carry an organelle-specific targeting signal for recognition by organelle-specific import machinery.However,the situation is confusing for transmembrane domain(TMD)-containing signalanchored(SA)proteins of various organelles because TMDs function as an endoplasmic reticulum(ER)targeting signal.Although ER targeting of SA proteins is well understood,how they are targeted to mitochondria and chloroplasts remains elusive.Here,we investigated how the targeting specificity of SA proteins is determined for specific targeting to mitochondria and chloroplasts.Mitochondrial targeting requires multiple motifs around and within TMDs:a basic residue and an arginine-rich region flanking the N-and C-termini of TMDs,respectively,and an aromatic residue in the C-terminal side of the TMD that specify mitochondrial targeting in an additive manner.These motifs play a role in slowing down the elongation speed during translation,thereby ensuring mitochondrial targeting in a cotranslational manner.By contrast,the absence of any of these motifs individually or together causes at varying degrees chloroplast targeting that occurs in a post-translational manner.

Understanding protein translocation across chloroplast membranes:Translocons and motor proteins

Subcellular organelles in eukaryotes are surrounded by lipid membranes.In an endomembrane system,vesicle trafficking is the primary mechanism for the delivery of organellar proteins to specific organelles.However,organellar proteins for chloroplasts,mitochondria,the nucleus,and peroxisomes that are translated in the cytosol are directly imported into their target organelles.Chloroplasts are a plant-specific organelle with outer and inner envelope membranes,a dual-membrane structure that is similar to mitochondria.Interior chloroplast proteins translated by cytosolic ribosomes are thus translocated through TOC and TIC complexes(translocons in the outer and inner envelope of chloroplasts,respectively),with stromal ATPase motor proteins playing a critical role in pulling pre-proteins through these import channels.Over the last three decades,the identity and function of TOC/TIC components and stromal motor proteins have been actively investigated,which has shed light on the action mechanisms at a molecular level.However,there remains some disagreement over the exact composition of TIC complexes and genuine stromal motor proteins.In this review,we discuss recent findings on the mechanisms by which proteins are translocated through TOC/TIC complexes and discuss future prospects for this field of research.

Molecular Mechanism of the Specificity of Protein Import into Chloroplasts and Mitochondria in Plant Cells

Plants possess both types of endosymbiotic organelles, chloroplasts and mitochondria. Transit peptides and presequences function as signal sequences for specific import into chloroplasts and mitochondria, respectively. However, how these highly similar signal sequences confer the protein import specificity remains elusive. Here, we show that mitochondrial- or chloroplast-specific import involves two distinct steps, specificity determination and translocation across envelopes, which are mediated by the N-terminal regions and functionally interchangeable C-terminal regions, respectively, of transit peptides and presequences. A domain harboring multiple-arginine and hydrophobic sequence motifs in the N-terminal regions of presequences was identified as the mitochondrial specificity factor. The presence of this domain and the absence of arginine residues in the N-terminal regions of otherwise common targeting signals confers specificity of protein import into mitochondria and chloroplasts, respectively. AtToc159, a chloroplast import receptor, also contributes to determining chloroplast import specificity. We propose that common ancestral sequences were functionalized into mitochondrial- and chloroplast-specific signal sequences by the presence and absence, respectively, of multiple-arginine and hydrophobic sequence motifs in the N-terminal region.

Interactions between Transmembrane Helices within Monomers of the Aquaporin AtPIP2;1 Play a Crucial Role in Tetramer Formation

Aquaporin （AQP） is a water channel protein found in various subcellular membranes of both prokaryotic and eukaryotic cells. The physiological functions of AQPs have been elucidated in many organisms. However, understanding their biogenesis remains elusive, particularly regarding how they assemble into tetramers. Here, we investigated the amino acid residues involved in the tetramer formation of the Arabidopsis plasma membrane AQP AtPIP2;1 using extensive amino acid substitution mutagenesis. The mutant proteins V41A/ E44A, F51A/L52A, F87A/191A, F92A/193A, V95A/Y96A, and H216A/L217A, harboring alanine substitutions in the transmembrane （TM） helices of AtPIP2;1 polymerized into multiple oligomeric complexes with a vari- able number of subunits greater than four. Moreover, these mutant proteins failed to traffic to the plasma membrane, instead of accumulating in the endoplasmic reticulum （ER）. Structure-based modeling revealed that these residues are largely involved in interactions between TM helices within monomers. These results suggest that inter-TM interactions occurring both within and between monomers play crucial roles in tetramer formation in the AtPIP2;1 complex. Moreover, the assembly of AtPIP2;1 tetramers is critical for their trafficking from the ER to the plasma membrane, as well as water permeability.

Cytochrome b5 Reductase 1 Triggers Serial Reactions that Lead to Iron Uptake in Plants

Rhizosphere acidification is essential for iron （Fe） uptake into plant roots. Plasma membrane （PM） H＊-ATPases play key roles in rhizosphere acidification. However, it is not fully understood how PM H＋-ATPase activity is regulated to enhance root Fe uptake under Fe-deficient conditions. Here, we present evidence that cytochrome b5 reductase 1 （CBR1） increases the levels of unsaturated fatty acids, which stimulate PM H＋-ATPase activity and thus lead to rhizosphere acidification. CBRl-overexpressing （CBRI-OX） Arabidopsis thaliana plants had higher levels of unsaturated fatty acids （18：2 and 18：3）, higher PM H＊-ATPase activity, and lower rhizosphere pH than wild-type plants. By contrast, cbrl loss-of-function mutant plants showed lower levels of unsaturated fatty acids and lower PM H＊-ATPase activity but higher rhizosphere pH. Reduced PM H＊-ATPase activity in cbrl could be restored in vitro by addition of unsatu- rated fatty acids. Transcript levels of CBR1, fatty acids desaturase 2 （FAD2）, and fatty acids desaturase 3 （FAD3） were increased under Fe-deficient conditions. We propose that CBR1 has a crucial role in increasing the levels of unsaturated fatty acids, which activate the PM H＊-ATPase and thus reduce rhizosphere pH. This reaction cascade ultimately promotes root Fe uptake.

Arabidopsis BAG1 Functions as a Cofactor in Hsc70-Mediated Proteasomal Degradation of Unimported Plastid Proteins

Dear Editor,Eliminating misfolded or mistargeted proteins is crucial for cell viability because these proteins accumulate as non-specific aggregates, which can be toxic to the cell （Lee et al., 2009; Sroka et al., 2009）. Previously, we have shown that in ppi2 （plastid protein import 2） mutant plants, the transcript levels of Hsc70-4 （one isoform of the Hsc70 family） and CHIP （an E3 ligase） were highly upregulated, which ultimately plays crucial roles in proteasomal degradation of unimported plastid proteins （Lee et al., 2009）. We also found that, along with those of Hsc70-4 and CHIP, the transcript level of AtBAG1 （Arabidopsis thaliana Bcl2-associated athanogene 1） in the ppi2 mutant was 2.38-fold higher than that in the wild-type （Lee et al., 2009）.

Nanostructured hafnium-doped strontium oxide film for homeotropic/homogeneous convertible liquid crystal alignment depending on the curing temperature

A hafnium strontium oxide(HfSrO)liquid crystal(LC)alignment film was efficiently created through brush coating,and its ability to change the LC alignment direction was confirmed.A brush was applied to HfSrO sol coated on an indium-tin oxide substrate,after which the coating was solidified at var-ious curing temperatures.It was confirmed that a directional micro/nanostructure was formed above 280°C due to the shear stresses caused by the movement of the brush hairs.Surface chemical changes were analyzed by using X-ray photoelectron spectroscopy and contact angle measurements.As the curing temperature increased,the prevalence of oxygen bonds increased and the contact angle decreased,thereby increasing the surface energy.The anisotropic boundary of the micro-grooves and the van der Waals forces due to an increase in surface energy changed the alignment direction of LC mole-cules from vertical to horizontal,as verified through polarized optical microscopy and pretilt angle measurements.Thus,the efficiency of the brush-coating method,which dramatically simplifies the LC alignment film process,was confirmed.The homeotropic/homogeneous LC alignment property of the HfSrO film produced through brush coating depending on the curing temperature provides an innovative approach for LC alignment.

Liquid-Liquid Phase Transition as a New Means of Protein Targeting in Chloroplasts

The chloroplast is a unique organelle in that it possesses an intra-organellar membrane-enclosed structure called thylakoid,which is central to photosynthesis.Thus,the timely expression and correct localization of thylakoid proteins are of utmost importance to plant growth and development(Lee et al.,2017;New et al.,2018).Biogenesis of thylakoid proteins is highly complex;they are encoded by two different genomes,nuclear and chloroplast genomes,and translated in the cytosol and chloroplasts,respectively.Nuclear-encoded thylakoid proteins are first imported into the stroma of chloroplasts before they are targeted to thylakoids.In the stroma,multiple sorting mechanisms exist to ensure import or insertion of thylakoid luminal or membrane proteins,respectively(Lee et al.,2017).Approximately 50%of thylakoid luminal proteins are imported through the cpTAT(chloroplast twin-arginine translocation)pathway,which is also present in bacteria and plant mitochondria(Cline,2015;Schafer et al.f 2020).