Renal Failure Without Hemodialysis Is a Risk Factor for Postoperative Complications in Colorectal Cancer Surgery.

Background/Aim: Surgical outcomes of colorectal cancer (CRC) in patients with renal failure (RF) remain to be clarified. The objective of this research was to investigate how RF impacts the surgical outcomes in patients with CRC. Patients and Methods: A retrospective analysis was performed on clinical data from 633 patients who underwent colorectal resection for CRC between January 2017 and December 2021. Outcomes of the patients with and without RF were compared. RF was defined as estimated Glomerular Filtration Rate less than 30. Results: Forty-five (7%) patients with RF were identified. RF was a significant risk factor for postoperative complications after colorectal cancer surgery (odds ratio=2.19, 95% confidence interval=1.08-4.42, p=0.0284). The patients with RF had significantly more comorbidity (p=0.016), and higher American Society of Anesthesiologists physical status (p<0.01). Hemoglobin level (p<0.01) and PNI (p<0.01) were significantly lower in those with RF. Postoperative complications were significantly higher (p=0.016), and the postoperative hospital stay was significantly longer (p<0.01) among patients with RF compared to those without RF. Patients with RF, excluding those undergoing hemodialysis, had significantly more complications compared to those without RF (p=0.004). Conclusion: Careful attention should be paid to perioperative management in RF colorectal cancer patients.

MucA is a small peptide encoded by an overlapping sequence with cdsA that upregulates the biosynthesis of glycolipid MPIase in the cold.

MPIase is a glycolipid involved in protein insertion into and preprotein translocation across the cytoplasmic membranes of E. coli. MPIase is upregulated in the cold conditions to overcome the cold-sensitive protein export. CdsA, a CDP-diacylglycerol synthase, catalyzes the first reaction in MPIase biosynthesis. An open reading frame for a peptide of 50 amino acids is encoded immediately after ispU, a neighboring upstream gene of cdsA, and overlaps cdsA to a large extent. Mutational analysis revealed that the expression of this peptide is essential for upregulation of MPIase in the cold. Consistently, expression of this peptide in trans resulted in cold upregulation of MPIase. We therefore named this peptide MucA after its function (MPIase upregulation in the cold). When the partially purified MucA was added to the reaction of the intermediate in MPIase biosynthesis, a significant increase in the product formation was observed, supporting the function of MucA. The possible role of MucA in MPIase biosynthesis is discussed.

CdsA, a CDP-diacylglycerol synthase involved in phospholipid and glycolipid MPIase biosynthesis, possesses multiple initiation codons.

CdsA is a CDP-diacylglycerol synthase essential for phospholipid and glycolipid MPIase biosynthesis, and therefore for growth. The initiation codon of CdsA has been assigned as "TTG," while methionine at the 37th codon was reported to be an initiation codon in the original report. Since a vector containing the open reading frame starting with "TTG" under a controllable promoter complemented the cdsA knockout, "TTG" could function as an initiation codon. However, no evidence supporting that this "TTG" is the sole initiation codon has been reported. We determined the initiation codon by examining the ability of mutants around the N-terminal region to complement cdsA mutants. Even if the "TTG" was substituted with a stop codon, the clear complementation was observed. Moreover, the clones with multiple mutations of stop codons complemented the cdsA mutant up to the 37th codon, indicating that cdsA possesses multiple codons that can function as initiation codons. We constructed an experimental system in which the chromosomal expression of cdsA can be analyzed. By means of this system, we found that the cdsA mutant with substitution of "TTG" with a stop codon is fully functional. Thus, we concluded that CdsA contains multiple initiation codons.

Coordinated upregulation of two CDP-diacylglycerol synthases, YnbB and CdsA, is essential for cell growth and membrane protein export in the cold.

YnbB is a paralogue of CdsA, a CDP-diacylglycerol synthase. While the cdsA gene is essential, the ynbB gene is dispensable. So far, no phenotype of ynbB knockout has been observed. We found that a ynbB knockout strain acquired cold-sensitivity on growth under CdsA-limited conditions. We found that MPIase, a glycolipid involved in protein export, is cold-upregulated to facilitate protein export in the cold, by increasing the mRNA levels of not only CdsA but also that of YnbB. Under non-permissive conditions, phospholipid biosynthesis proceeded normally, however, MPIase upregulation was inhibited with accumulation of precursors of membrane and secretory proteins such as M13 procoat and proOmpA, indicating that YnbB is dedicated to MPIase biosynthesis, complementing the CdsA function.

Hysterectomy through Minimally Invasive Surgery for Cervical High-grade Intraepithelial Neoplasia: Reassessment of the Specimens' Eligibility for Histological Examination.

Objectives: The objective was to investigate the microscopic artifacts made in the uterus of cervical high-grade squamous intraepithelial lesion (HSIL) resected by hysterectomy through minimally invasive (H-MI) procedures and to verify whether these specimens are suitable for histopathological assessment. Materials and Methods: This single-center retrospective study analyzed 28 patients with cervical HSIL, consisting of 21 premenopausal and seven postmenopausal women, who underwent H-MI. The proportion of the cervical mucosa covered by intact surface epithelium (residual ratio [RR]) was measured on microscopically. Surgical margin's status was also verified. Results: All cases developed detachment of the cervical surface epithelium to a varying extent. The RR was significantly higher in the premenopausal patients (median: 75.5%) than in the postmenopausal patients (median: 37.6%). Among the premenopausal patients, the RR was lower in the cases on whom uterine manipulator (UM) was used (median: 70.5%) than in the cases without UM use (median 92.7%). Among the 21 cases whose resected uterus contained HSIL, the vaginal resection margin was not assessable in three (14.2%) of the seven postmenopausal cases due to the artifact. Conclusion: Although transvaginal manipulation of the uterus causes detachment of the cervical surface epithelium, H-MI for cervical HSIL provides an acceptable specimen for histological assessment in premenopausal patients, even if UM is used. In postmenopausal women, H-MI easily develops artifactual loss of cervical surface epithelium, sometimes providing an unfavorable specimen for microscopic assessment.

Long-Term Safety, Tolerability, and Efficacy of a Transdermal Donepezil Patch in Patients with Severe Alzheimer's Disease.

BACKGROUND: Oral formulations are not suitable for demented patients with dysphagia, those refuse to take tablets, or those with drug compliance problem. However, only oral formulations of donepezil hydrochloride are approved for the treatment of severe Alzheimer's disease in Japan. OBJECTIVE: To evaluate the safety, tolerability, and efficacy of long-term application of a 55.0 mg transdermal donepezil patch switched from a 10 mg oral donepezil hydrochloride tablet, for the treatment of patients with severe Alzheimer's disease. METHODS: A 52-week, multicenter, open-label, uncontrolled (phase III) study (jRCT2080224612) was conducted in Japan between April 2019 and August 2021. A 10 mg donepezil hydrochloride tablet was administered once a day for four weeks; a 55.0 mg donepezil patch was then applied once a day for 52 weeks in patients with severe Alzheimer's disease. RESULTS: Of 64 patients received the patch, 45 completed the 52-week period. The overall discontinuation rate was 29.7% (19/64). Among the 19 patients discontinued, six patients 9.4% (6/64) discontinued due to adverse events. The incidence of adverse events at application sites was 67.2% (43/64), including application site erythema 29.7% (19/64), application site pruritus 25.0% (16/64), and contact dermatitis 20.3% (13/64). Adverse events were mild and did not increase with time, demonstrating a favorable safety profile. Cognitive function, measured using the Mini-Mental State Examination, was maintained for up to 24 weeks. CONCLUSIONS: Adverse events were considered manageable in a clinical setting. The long-term application of a 55.0 mg donepezil patch once a day was feasible treatment in patients with severe Alzheimer's disease.

Efficacy and Safety of a Transdermal Donepezil Patch in Patients with Mild to Moderate Alzheimer's Disease: Open-Label, Extension Study.

BACKGROUND: In Japan, only oral formulation of donepezil hydrochloride is approved for the treatment of Alzheimer's disease. OBJECTIVE: To evaluate safety and efficacy of a donepezil patch 27.5 mg application for 52 weeks in patients with mild-to-moderate Alzheimer's disease; and to evaluate safety on switching from donepezil hydrochloride tablets. METHODS: This 28-week, open-label study (jRCT2080224517) is an extension of a 24-week double-blind (donepezil patch 27.5 mg versus donepezil hydrochloride tablet 5 mg) noninferiority study. The patch group (continuation group) continued administration of the patch and the tablet group (switch group) switched to the patch in this study. RESULTS: A total of 301 patients participated (156 patients continued using patches; 145 patients switched). Both groups showed similar course on the Alzheimer's Disease Assessment Scale-cognitive component-Japanese version (ADAS-Jcog) and ABC dementia scales. At weeks 36 and 52, changes in ADAS-Jcog from week 24 [mean (standard deviation)] were 1.4 (4.8) and 2.1 (4.9) in the continuation group, and 1.0 (4.2), and 1.6 (5.4) in the switch group. The incidence of adverse events at application site in the continuation group over 52 weeks was 56.6% (98/173). Erythema, pruritus, and contact dermatitis at application site were observed in more than 10 patients each. There was no additional adverse event of clinical concern, and no increase in their incidence from the double-blind study. During the four weeks following switching, no patient discontinued or suspended administration due to adverse events. CONCLUSION: Application of the patch for 52 weeks was well tolerated and feasible, including switching from tablets.

Structural Requirements of a Glycolipid MPIase for Membrane Protein Integration.

MPIase is a glycolipid involved in membrane protein integration in the inner membrane of Escherichia coli. To overcome the trace amounts and heterogeneity of natural MPIase, we systematically synthesized MPIase analogs. Structure-activity relationship studies revealed the contribution of distinctive functional groups and the effect of the MPIase glycan length on membrane protein integration activity. In addition, both the synergistic effects of these analogs with the membrane chaperone/insertase YidC, and the chaperone-like activity of the phosphorylated glycan were observed. These results verified the translocon-independent membrane integration mechanism in the inner membrane of E. coli, in which MPIase captures the highly hydrophobic nascent proteins via its characteristic functional groups, prevents protein aggregation, attracts the proteins to the membrane surface, and delivers them to YidC in order to regenerate its own integration activity.

Efficacy and safety of a transdermal donepezil patch in patients with mild-to-moderate Alzheimer's disease: A 24-week, randomized, multicenter, double-blind, parallel group, non-inferiority study.

AIM: To assess non-inferiority of a donepezil patch 27.5 mg compared with donepezil hydrochloride tablets 5 mg in patients with mild-to-moderate Alzheimer's disease; and to compare the efficacy and safety profiles of a donepezil patch 27.5 mg with donepezil hydrochloride tablets 5 mg. METHODS: This was a 24-week, multicenter, randomized, double-blind, double-dummy, parallel group, non-inferiority (phase III) study carried out in Japan. The primary end-point was the change in the Alzheimer's Disease Assessment Scale-cognitive component-Japanese version from baseline to week 24, with the aim of evaluating the non-inferiority of the donepezil patch 27.5 mg compared with donepezil hydrochloride tablets 5 mg. RESULTS: Of 340 randomized patients, 303 completed the double-blind period. Changes from baseline in the Alzheimer's Disease Assessment Scale-cognitive component-Japanese version at week 24 (least squares mean ± standard error) were -0.7 ± 0.4 (donepezil patch 27.5 mg) and 0.2 ± 0.4 (donepezil hydrochloride tablet 5 mg). The difference in the least squares means (95% confidence interval) was -0.9 (-2.01 to 0.14). The upper bound of the 95% confidence interval for the difference between groups was less than the predefined non-inferiority margin of 2.15. The donepezil patches 27.5 mg also had a safety profile that showed good tolerability comparable with donepezil hydrochloride tablets 5 mg. CONCLUSIONS: Non-inferiority on suppression of cognitive decline was shown for the donepezil patch 27.5 mg when compared with donepezil hydrochloride tablets 5 mg in Japanese patients with mild-to-moderate Alzheimer's disease. Geriatr Gerontol Int 2023; 23: 275-281.

Comparative analyses of tumour immune microenvironment between collecting duct carcinoma and fumarate hydratase-deficient renal cell carcinoma.

AIMS: Collecting duct carcinoma (CDC) and fumarate hydratase-deficient renal cell carcinoma (FH-deficient RCC) have similar histological morphologies and both show a poor prognosis. Programmed death ligand 1 (PD-L1) inhibitor has been approved for the treatment of RCC. However, tumour-infiltrating neutrophils stimulated by interleukin-8 (IL-8) interfere with PD-L1 inhibitors. Here, we retrospectively analysed PD-L1 and IL-8 expression, and examined its relationship with infiltrating immune cells. METHODS: Nine cases of CDC and seven cases of FH-deficient RCC were selected. We defined PD-L1 and IL-8 expression by the Tumour Proportion Score and Combined Positive Score (CPS). We counted the numbers of CD8+, CXCR2+, CD11b+, CD66b+ and CD33+ immune cells located in the tumour components. RESULTS: A number of CXCR2+ (p=0.0058), CD11b+ (p=0.0070) and CD66b+ (p=0.0067) immune cells infiltrating into CDC were significantly higher than those infiltrating into FH-deficient RCC. In CDC, PD-L1 expression was correlated with a high density of CD8+ lymphocytes (p=0.0389), but was not in FH-deficient RCC (p=0.6985). IL-8 CPS was significantly higher in CDC than in FH-deficient RCC (p=0.0069). In addition, among the CDC cases, IL-8 CPS showed significant positive correlations with CXCR2+, CD11b+ and CD66b+ immune cell densities (p=0.0250, p=0.0104 and p=0.0374, respectively), whereas FH-deficient RCC showed no significant correlations between IL-8 CPS and immune cell densities. CONCLUSIONS: Our results suggest the difference of each tumour microenvironment between CDC and FH-deficient RCC, and IL-8 is a potential therapeutic target for treating CDC, but not FH-deficient RCC.

A bacterial glycolipid essential for membrane protein integration.

The proper conformation and orientation of membrane protein integration in cells is an important biological event. Interestingly, a new factor named MPIase (membrane protein integrase) was proven essential in this process in Escherichia coli, besides proteinaceous factors, such as Sec translocons and an insertase YidC. A combination of spectroscopic analyses and synthetic work has revealed that MPIase is a glycolipid despite its enzyme-like activity. MPIase has a long glycan chain comprised of repeating trisaccharide units, a pyrophosphate linker, and a diacylglycerol anchor. In order to determine the mechanism of its activity, we synthesized a trisaccharyl pyrophospholipid termed mini-MPIase-3, a minimal unit of MPIase, and its derivatives. A significant activity of mini-MPIase-3 indicated that it involves an essential structure for membrane protein integration. We also analyzed intermolecular interactions of MPIase or its synthetic analogs with a model substrate protein using physicochemical methods. The structure-activity relationship studies demonstrated that the glycan part of MPIase prevents the aggregation of substrate proteins, and the 6-O-acetyl group on glucosamine and the phosphate of MPIase play important roles for interactions with substrate proteins. MPIase serves at an initial step in the Sec-independent integration, whereas YidC, proton motive force, and/or SecYEG cooperatively function(s) with MPIase at the following step in vivo. Furthermore, depletion of the biosynthetic enzyme demonstrated that MPIase is crucial for membrane protein integration and cell growth. Thus, we elucidated new biological functions of glycolipids using a combination of synthetic chemistry, biochemistry, physicochemical measurements, and molecular-biological approaches.

Interaction between glycolipid MPIase and proteinaceous factors during protein integration into the cytoplasmic membrane of E. coli.

Protein integration into biomembranes is an essential biological phenomenon common to all organisms. While various factors involved in protein integration, such as SRP, SecYEG and YidC, are proteinaceous, we identified a glycolipid named MPIase (Membrane Protein Integrase), which is present in the cytoplasmic membrane of E. coli. In vitro experiments using inverted membrane vesicles prepared from MPIase-depleted strains, and liposomes containing MPIase showed that MPIase is required for insertion of a subset of membrane proteins, which has been thought to be SecYEG-independent and YidC-dependent. Also, SecYEG-dependent substrate membrane proteins require MPIase in addition. Furthermore, MPIase is also essential for insertion of proteins with multiple negative charges, which requires both YidC and the proton motive force (PMF). MPIase directly interacts with SecYEG and YidC on the membrane. MPIase not only cooperates with these factors but also has a molecular chaperone-like function specific to the substrate membrane proteins through direct interaction with the glycan chain. Thus, MPIase catalyzes membrane insertion by accepting nascent membrane proteins on the membrane through its chaperone-like function, i.e., direct interaction with the substrate proteins, and then MPIase functionally interacts with SecYEG and YidC for substrate delivery, and acts with PMF to facilitate and complete membrane insertion when necessary. In this review, we will outline the mechanisms underlying membrane insertion catalyzed by MPIase, which cooperates with proteinaceous factors and PMF.

Role of a bacterial glycolipid in Sec-independent membrane protein insertion.

Non-proteinaceous components in membranes regulate membrane protein insertion cooperatively with proteinaceous translocons. An endogenous glycolipid in the Escherichia coli membrane called membrane protein integrase (MPIase) is one such component. Here, we focused on the Sec translocon-independent pathway and examined the mechanisms of MPIase-facilitated protein insertion using physicochemical techniques. We determined the membrane insertion efficiency of a small hydrophobic protein using solid-state nuclear magnetic resonance, which showed good agreement with that determined by the insertion assay using an in vitro translation system. The observed insertion efficiency was strongly correlated with membrane physicochemical properties measured using fluorescence techniques. Diacylglycerol, a trace component of E. coli membrane, reduced the acyl chain mobility in the core region and inhibited the insertion, whereas MPIase restored them. We observed the electrostatic intermolecular interactions between MPIase and the side chain of basic amino acids in the protein, suggesting that the negatively charged pyrophosphate of MPIase attracts the positively charged residues of a protein near the membrane surface, which triggers the insertion. Thus, this study demonstrated the ingenious approach of MPIase to support membrane insertion of proteins by using its unique molecular structure in various ways.

[Theory and Practice of Endoscopic Third Ventriculostomy].

Endoscopic third ventriculostomy(ETV)is a basic procedure for the surgical treatment of hydrocephalus. It buffers pulsatile pressure by creating an alternative route for the flow of cerebrospinal fluid and reduces trans-mantle pulsatile stress, thereby increasing compliance of the brain parenchyma. Blunt perforation of the third ventricular floor is done while avoiding injury to the foramen of Monro, the hypothalamus, the pituitary stalk, and some cisternal vessels. A major complication of ETV is arterial bleeding caused by injury to the basilar artery. Surgeons should wait with irrigation and opening the root into the ventricle to control the intra-ventricular pressure until packing the third ventricle with hematoma. Since ETV may close by gliosis or scarring of the inter-peduncular cistern, regular physical examinations and MRI should follow the procedure.

Intermolecular Interactions between a Membrane Protein and a Glycolipid Essential for Membrane Protein Integration.

Inducing newly synthesized proteins to appropriate locations is an indispensable biological function in every organism. Integration of proteins into biomembranes in Escherichia coli is mediated by proteinaceous factors, such as Sec translocons and an insertase YidC. Additionally, a glycolipid named MPIase (membrane protein integrase), composed of a long sugar chain and pyrophospholipid, was proven essential for membrane protein integration. We reported that a synthesized minimal unit of MPIase possessing only one trisaccharide, mini-MPIase-3, involves an essential structure for the integration activity. Here, to elucidate integration mechanisms using MPIase, we analyzed intermolecular interactions of MPIase or its synthetic analogs with a model substrate, the Pf3 coat protein, using physicochemical methods. Surface plasmon resonance (SPR) analyses revealed the importance of a pyrophosphate for affinity to the Pf3 coat protein. Compared with mini-MPIase-3, natural MPIase showed faster association and dissociation due to its long sugar chain despite the slight difference in affinity. To focus on more detailed MPIase substructures, we performed docking simulations and saturation transfer difference-nuclear magnetic resonance. These experiments yielded that the 6-O-acetyl group on glucosamine and the phosphate of MPIase play important roles leading to interactions with the Pf3 coat protein. The high affinity of MPIase to the hydrophobic region and the basic amino acid residues of the protein was suggested by docking simulations and proven experimentally by SPR using protein mutants devoid of target regions. These results demonstrated the direct interactions of MPIase with a substrate protein and revealed detailed mechanisms of membrane protein integration.

Approach for reclassification of collecting duct carcinoma and comparative histopathological analysis with SMARCB1/INI1-deficient renal cell carcinoma and fumarate hydratase-deficient renal cell carcinoma.

Collecting duct carcinoma (CDC) is a rare subset of high-grade renal cell carcinoma (RCC). To diagnose CDC, it is necessary to rule out other renal tumors including renal medullary carcinoma and fumarate hydratase (FH)-deficient RCC. However, there is overlap in the morphology of these three tumors, which all have poor outcomes. There is also still a need to sufficiently examine the therapeutic strategies for each of these tumors. In this study, we retrospectively reclassified invasive/infiltrating high-grade RCC and investigated its pathological features. We reviewed 18 cases previously diagnosed as "CDC," "FH-deficient RCC," and "unclassified RCC," which were reclassified as SMARCB1/INI1-deficient RCC, FH-deficient RCC, and CDC by SMARCB1/INI1, FH, and 2SC immunohistochemistry (IHC) and FH gene mutational status. As the result, 18 cases were reclassified into 2 cases of SMARCB1/INI1-deficient RCC, 7 cases of FH-deficient RCC, and 9 cases of CDC. The morphological features of each group overlapped, and no specific immunohistochemical expression except for SMARCB1/INI1, FH, and 2SC was detected. These results suggest that invasive/infiltrating high-grade RCC should be diagnosed by the combination of immunohistochemistry and molecular biological technique.

Histological background of dedifferentiated solitary fibrous tumour.

AIMS: Dedifferentiation is a histological phenomenon characterised by abrupt transition of histology to a sarcomatous component with high-grade malignant potential in solitary fibrous tumour (SFT). The authors histologically reviewed SFT cases to reveal the histological background of dedifferentiated SFTs. METHODS: Clinicopathological and histopathological findings of 145 SFT cases were reviewed. Immunohistochemical staining and genetic analysis were also performed. RESULTS: The non-dedifferentiated components showed a cellular component in 45 of 145 (31%), high mitotic rate (≥4/10 high-powered field) in 12 of 145 (8.2%) tumours, necrosis in 7 of 145 (4.8%) tumours, multinodular growth pattern in 39 of 132 (29.5%) available tumours and intratumoural fibrous septa in 37 of 131 (28.2%). Immunohistochemically, the non-dedifferentiated components were positive for CD34 in 128 of 141 (90.7%), bcl-2 in 101 of 133 (75.9%), nuclear pattern of ß-catenin in 64 of 127 (50.3%) and p16 in 22 of 140 (15.7%). Loss of Rb protein expression was detected in 17 of 110 (15.4%) cases. Statistically, cellular component, multinodular structure, p16 overexpression and Rb protein loss were significantly associated with dedifferentiation. Moreover, cellular component and multinodular structure were significantly associated with p16 overexpression and Rb protein loss. All the non-deddifferentiated components showed wild type of p53 expression. The dedifferentiated components of all 10 dedifferentiated tumours presented positivity for p16 in 9 of 10 (90%) and mutational type of p53 in 5 of 10 (50%). Loss of Rb protein expression was detected in 6 of 10 (60%). CONCLUSIONS: The authors propose that cellular or multinodular transformation may be associated with dedifferentiation. They also suggest that cellular and multinodular transformation may be associated with p16 overexpression and Rb downregulation.

Interplay between MPIase, YidC, and PMF during Sec-independent insertion of membrane proteins.

Integral membrane proteins with the N-out topology are inserted into membranes usually in YidC- and PMF-dependent manners. The molecular basis of the various dependencies on insertion factors is not fully understood. A model protein, Pf3-Lep, is inserted independently of both YidC and PMF, whereas the V15D mutant requires both YidC and PMF in vivo. We analyzed the mechanisms that determine the insertion factor dependency in vitro. Glycolipid MPIase was required for insertion of both proteins because MPIase depletion caused a significant defect in insertion. On the other hand, YidC depletion and PMF dissipation had no effects on Pf3-Lep insertion, whereas V15D insertion was reduced. We reconstituted (proteo)liposomes containing MPIase, YidC, and/or F0F1-ATPase. MPIase was essential for insertion of both proteins. YidC and PMF stimulated Pf3-Lep insertion as the synthesis level increased. V15D insertion was stimulated by both YidC and PMF irrespective of the synthesis level. These results indicate that charges in the N-terminal region and the synthesis level are the determinants of YidC and PMF dependencies with the interplay between MPIase, YidC, and PMF.

Expression of Cds4/5 of Arabidopsis chloroplasts in E. coli reveals the membrane topology of the C-terminal region of CDP-diacylglycerol synthases.

CDP-diacylglycerol synthases (Cds) are conserved from bacteria to eukaryotes. Bacterial CdsA is involved not only in phospholipid biosynthesis but also in biosynthesis of glycolipid MPIase, an essential glycolipid that catalyzes membrane protein integration. We found that both Cds4 and Cds5 of Arabidopsis chloroplasts complement cdsA knockout by supporting both phospholipid and MPIase biosyntheses. Comparison of the sequences of CdsA and Cds4/5 suggests a difference in membrane topology at the C-termini, since the region assigned as the last transmembrane region of CdsA, which follows the conserved cytoplasmic domain, is missing in Cds4/5. Deletion of the C-terminal region abolished the function, indicating the importance of the region. Both 6 × His tag attachment to CdsA and substitution of the C-terminal 6 residues with 6 × His did not affect the function. These 6 × His tags were sensitive to protease added from the cytosolic side in vitro, indicating that this region is not a transmembrane one but forms a membrane-embedded reentrant loop. Thus, the C-terminal region of Cds homologues forms a reentrant loop, of which structure is important for the Cds function.