Guard-Cell-Specific Expression of Phototropin2 C-Terminal Fragment Enhances Leaf Transpiration

Phototropins (phot1 and phot2) are plant-specific blue light receptors that mediate chloroplast movement, stomatal opening, and phototropism. Phototropin is composed of the N-terminus LOV1 and LOV2 domains and the C-terminus Ser/Thr kinase domain. In previous studies, 35-P2CG transgenic plants expressing the phot2 C-terminal fragment–GFP fusion protein (P2CG) under the control of 35S promoter showed constitutive phot2 responses, including chloroplast avoidance response, stomatal opening, and reduced hypocotyl phototropism regardless of blue light, and some detrimental growth phenotypes. In this study, to exclude the detrimental growth phenotypes caused by the ectopic expression of P2C and to improve leaf transpiration, we used the PHOT2 promoter for the endogenous expression of GFP-fused P2C (GP2C) (P2-GP2C) and the BLUS1 promoter for the guard-cell-specific expression of GP2C (B1-GP2C), respectively. In P2-GP2C plants, GP2C expression induced constitutive phototropin responses and a relatively dwarf phenotype as in 35-P2CG plants. In contrast, B1-GP2C plants showed the guard-cell-specific P2C expression that induced constitutive stomatal opening with normal phototropism, chloroplast movement, and growth phenotype. Interestingly, leaf transpiration was significantly improved in B1-GP2C plants compared to that in P2-GP2C plants and WT. Taken together, this transgenic approach could be applied to improve leaf transpiration in indoor plants.

Effect of Mutations in GvpJ and GvpM on Gas Vesicle Formation of Halobacterium salinarum

The two haloarchaeal proteins, GvpM and GvpJ, are homologous to GvpA, the major gas vesicle structural protein. All three are hydrophobic and essential for gas vesicle formation. The effect of mutations in GvpJ and GvpM was studied in Haloferax volcanii transformants by complementing the respective mutated gene with the remaining gvp genes and inspecting the cells for the presence of gas vesicles (Vac+). In case of GvpJ, 56 of 66 substitutions analyzed yielded Vac– ΔJ + Jmut transformants, indicating that GvpJ is very sensitive to alterations, whereas ten of the 38 GvpM variants resulted in Vac– ΔM + Mmut transformants. The variants were also tested by split-GFP for their ability to interact with their partner protein GvpL. Some of the alterations leading to a Vac– phenotype affected the J/L or M/L interaction. Also, the interactions J/A and J/M were studied using fragments to exclude an unspecific aggregation of these hydrophobic proteins. Both fragments of GvpJ interacted with the M1–25 and M60–84 fragments of GvpM, and fragment J1–56 of GvpJ interacted with the N-terminal fragment A1–22 of GvpA. A comparison of the results on the three homologous proteins indicates that despite their relatedness, GvpA, GvpJ, and GvpM have unique features and cannot substitute each other.

Pyroptosis: Mechanisms and Links with Fibrosis

Fibrosis is responsible for approximately 45% of deaths in the industrialized world and has been a major global healthcare burden. Excessive fibrosis is the primary cause of organ failure. However, there are currently no approved drugs available for the prevention or treatment of fibrosis-related diseases. It has become evident that fibrosis is characterized by inflammation. In a large number of studies of various organs in mice and humans, pyroptosis has been found to play a significant role in fibrosis. Pyroptosis is a form of programmed cell death mediated by the N-terminal fragment of cysteinyl aspartate-specific proteinase (caspase)-1-cleaved gasdermin D (GSDMD, producing GSDMD-N) that gives rise to inflammation via the release of some proinflammatory cytokines, including IL-1β, IL-18 and HMGB1. These cytokines can initiate the activation of fibroblasts. Inflammasomes, an important factor upstream of GSDMD, can activate caspase-1 to trigger the maturation of IL-1β and IL-18. Moreover, the inhibition of inflammasomes, proinflammatory cytokines and GSDMD can prevent the progression of fibrosis. This review summarizes the growing evidence indicating that pyroptosis triggers fibrosis, and highlights potential novel targets for antifibrotic therapies.

DUAL FUNCTION OF ZIKA VIRUS NS2B-NS3 PROTEASE

Zika virus (ZIKV) serine protease, indispensable for viral polyprotein processing and replication, is composed of an NS2B polypeptide that associates with a proteolytic N terminal fragment of NS3 polypeptide (NS3pro) to form NS2B-NS3pro. The larger C-terminal fragment of NS3 polypeptide contains helicase activity. In the present study, we discovered that ZIKV NS2BNS3pro efficiently binds single-stranded (ss) RNA (Kd ~0.3 uM), suggesting that the protease may have a novel function. We tested an array of NS2B-NS3pro modifications and found that NS2B NS3pro constructs that adopt the recently discovered super-open conformation could not bind ssRNA. Likewise, stabilization of NS2B-NS3pro in the closed (proteolytically active) conformation by substrate-like inhibitors abolished ssRNA binding. Therefore, we suggest that ssRNA binding occurs when ZIKV protease adopts the open conformation, which could be modeled using dengue NS2B-NS3pro in the open conformation. ssRNA binding competes with ZIKV NS2B-NS3pro protease activity, likely by shifting the complex into the open conformation. Modeling of ZIKV NS3 helicase activity based on homologous crystal structures suggests that the open conformation of NS3pro domains provides a positively charged surface contiguous with the NS3 helicase domain. Such a positively charged surface is well poised to bind ssRNA, providing an explanation for the previously observed requirement of NS3pro for RNA processivity by viral helicase. Our structure-function analyses suggest that binding of ssRNA by the protease domain of NS3 is likely to be a universal feature of Flaviviridae, given the high level of homology between NS3 protease-helicase proteins in this family.

The extracellular β-glucosidase BGL2 has two variants with different molecular sizes and hydrolytic activities in the stipe or pilei of Coprinopsis cinerea

Two variants of extracellular β-glucosidase (BGL2) were purified from the stipe and pilei of Coprinopsis cinerea. In the stipe, BGL2 was a monomeric protein with an apparent molecular mass of approximately 220 kDa, representing a mature full-length peptide of BGL2. However, in the pilei, the apparent molecular mass of BGL2 was only approximately 120 kDa, consisting of the 60 kDa N-terminal fragment and 55 kDa C-terminal fragment. The hydrolytic activities of BGL2 purified from the pilei were higher than those of BGL2 purified from the stipe. No mRNA splice variants of bgl2 were detected. Therefore, the different variants of BGL2 in the stipe and pilei were not formed by differential RNA splicing. Furthermore, in vitro experiments showed that full-length BGL2 could be cleaved by endogenous proteases from pilei or commercial trypsin at a similar site to form an oligomeric protein consisting of the N-terminal fragment and C-terminal fragment similar to BGL2 from pilei. The hydrolytic activity of BGL2 increased after cleavage by those proteases in vitro. We conclude that the 120 kDa variant of BGL2 in the pilei of C. cinerea is formed by posttranslational proteolytic cleavage. Posttranslational proteolytic cleavage is an efficient way to regulate the activity of BGL2 to adapt to the needs of different physiological functions in the elongation stipe and expansion pilei of C. cinerea.

Fragmentation and roles of junctophilin1 in muscle of patients with cytosolic leak of stored calcium

The mechanisms that link the primary increase in SR Ca2+ leak of MH susceptibility and related conditions to their disease phenotypes are not well understood. We found that abnormal Ca2+ homeostasis in MHS individuals induces proteolysis of junctophilin1 (JPh1), an essential structural protein of EC coupling (Perni, in 2017). Guo (in 2018) and Lahiri (in 2020) reported similar fragmentation of JPh2 in stressed hearts. Western blot of patients’ muscle with domain-specific antibodies showed a deficit of full-length JPh1 and excess of a 44-kD C-terminal fragment (JPh44) in MHS subjects. While JPh1 was located in T-SR junctions, JPh44 was found anywhere within the I band, and at high densities within nuclei—a location forbidden for JPh1. Expression and cleavage in mice of a JPh1 plasmid tagged at both ends showed that its N-terminal fragment remained in triads, and the C-terminal fragment, orthologue to JPh44, entered nuclei, which indicates that JPh44 is the C-terminal cleavage product. Endogenous calpain1 appeared in T-SR junctions, colocalized with JPh1. On muscle extracts and primary cultures, Ca2+-activated calpain1 cleaved a 44-kD JPh1 piece, consistent with the C-terminal fragment that starts at Ser241, the highest probability cleavage site found by calpain1 algorithms. Completing the identification of Ser241 as the likely start of JPh44, the tagged deletion plasmid GFP-JPh1_Δ1-240, expressed in mice, copied the location and migration of JPh44. Expression of GFP-JPh1_Δ1-240 in C2C12 myoblasts reduced by more than twofold the transcription of PI3K-Akt genes that inhibit muscle uptake and storage of glucose, including GSK3β, an inhibitor of glycogen synthase that is activated in MHS patients. In agreement with the genetic profile, GSK3β protein content decreased upon expression of GFP-JPh1_Δ1-240. In sum, the identified gene control roles of JPh44 oppose the deleterious effects of chronically elevated cytosolic [Ca2+], including late-onset hyperglycemia and type-2 diabetes (Tammineni, in 2020).

CSIG-07. ACTIVATION OF THE ADHESION G PROTEIN-COUPLED RECEPTOR GPR133 BY ANTIBODIES AGAINST THE N-TERMINUS

We recently demonstrated that GPR133 (ADGRD1), a member of the adhesion G protein-coupled receptor (aGPCR) family, is necessary for growth of glioblastoma (GBM) and is de novo expressed in GBM relative to normal brain tissue. We therefore postulate that GPR133 represents a novel target in GBM, which merits development of therapeutics. Like most aGPCRs, GPR133 is characterized by an intracellular C-terminus, 7 plasma membrane-spanning α-helices and a large extracellular N-terminus. The N-terminus possesses a conserved GPCR autoproteolysis-inducing (GAIN) domain that catalyzes cleavage at a GPCR proteolysis site (GPS), resulting in a C-terminal fragment (CTF) and an N-terminal fragment (NTF). We showed that dissociation of the cleaved NTF and CTF at the plasma membrane increases canonical signaling of GPR133, which is mediated by coupling to Gs and increase in cytosolic cAMP. Toward characterizing the effect of biologics on GPR133 function, we overexpressed wild-type or mutant forms of GPR133 in HEK293T cells and patient-derived GBM cells lines. Treatment of these cells with antibodies specifically targeting the NTF of GPR133 increased receptor activation in a dose-dependent manner. No effects were elicited with an antibody against the receptor’s intracellular C-terminus. Interestingly, cells overexpressing a cleavage-deficient mutant GPR133 (H543R) did not respond to antibody stimulation, suggesting that the effect is cleavage-dependent. Following antibody treatment, co-purification of the GPR133 NTF and the N-terminal antibody from the cell culture supernatant indicated the formation of antibody-NTF complexes. Analysis of these complexes suggested that antibody binding stimulated the dissociation of the NTF from the CTF. However, the increased flexibility of the GAIN domain and NTF after cleavage, independently of dissociation, may also endow the receptor with responsiveness to the effects of the antibodies. These data constitute a proof-of-concept paradigm of modulation of GPR133 function with antibodies. This work provides rationale for pursuing development of biologics targeting GPR133 in GBM.

Protein PGLYRP1/Tag7 Peptides Decrease the Proinflammatory Response in Human Blood Cells and Mouse Model of Diffuse Alveolar Damage of Lung through Blockage of the TREM-1 and TNFR1 Receptors

Infection caused by the severe acute respiratory syndrome coronavirus (SARS-CoV-2) in many cases is accompanied by the release of a large amount of proinflammatory cytokines in an event known as “cytokine storm”, which is associated with severe coronavirus disease 2019 (COVID-19) cases and high mortality. The excessive production of proinflammatory cytokines is linked, inter alia, to the enhanced activity of receptors capable of recognizing the conservative regions of pathogens and cell debris, namely TLRs, TREM-1 and TNFR1. Here we report that peptides derived from innate immunity protein Tag7 inhibit activation of TREM-1 and TNFR1 receptors during acute inflammation. Peptides from the N-terminal fragment of Tag7 bind only to TREM-1, while peptides from the C-terminal fragment interact solely with TNFR1. Selected peptides are capable of inhibiting the production of proinflammatory cytokines both in peripheral blood mononuclear cells (PBMCs) from healthy donors and in vivo in the mouse model of acute lung injury (ALI) by diffuse alveolar damage (DAD). Treatment with peptides significantly decreases the infiltration of mononuclear cells to lungs in animals with DAD. Our findings suggest that Tag7-derived peptides might be beneficial in terms of the therapy or prevention of acute lung injury, e.g., for treating COVID-19 patients with severe pulmonary lesions.