1
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Fong C, Kueh WL, Lew SJW, Ho BCH, Wong YL, Lau YH, Chia YW, Tan HL, Seet YHC, Siow WT, MacLaren G, Agrawal R, Lim TJ, Lim SL, Lim TW, Ho VK, Soh CR, Sewa DW, Loo CM, Khan FA, Tan CK, Gokhale RS, Siau C, Lim NLSH, Yim CF, Venkatachalam J, Venkatesan K, Chia NCH, Liew MF, Li G, Li L, Myat SM, Zena Z, Zhuo S, Yueh LL, Tan CSF, Ma J, Yeo SL, Chan YH, Phua J. Predictors and outcomes of withholding and withdrawal of life-sustaining treatments in intensive care units in Singapore: a multicentre observational study. J Intensive Care 2024; 12:13. [PMID: 38528556 DOI: 10.1186/s40560-024-00725-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2024] [Accepted: 03/13/2024] [Indexed: 03/27/2024] Open
Abstract
BACKGROUND Clinical practice guidelines on limitation of life-sustaining treatments (LST) in the intensive care unit (ICU), in the form of withholding or withdrawal of LST, state that there is no ethical difference between the two. Such statements are not uniformly accepted worldwide, and there are few studies on LST limitation in Asia. This study aimed to evaluate the predictors and outcomes of withholding and withdrawal of LST in Singapore, focusing on the similarities and differences between the two approaches. METHODS This was a multicentre observational study of patients admitted to 21 adult ICUs across 9 public hospitals in Singapore over an average of three months per year from 2014 to 2019. The primary outcome measures were withholding and withdrawal of LST (cardiopulmonary resuscitation, invasive mechanical ventilation, and vasopressors/inotropes). The secondary outcome measure was hospital mortality. Multivariable generalised mixed model analysis was used to identify independent predictors for withdrawal and withholding of LST and if LST limitation predicts hospital mortality. RESULTS There were 8907 patients and 9723 admissions. Of the former, 80.8% had no limitation of LST, 13.0% had LST withheld, and 6.2% had LST withdrawn. Common independent predictors for withholding and withdrawal were increasing age, absence of chronic kidney dialysis, greater dependence in activities of daily living, cardiopulmonary resuscitation before ICU admission, higher Acute Physiology and Chronic Health Evaluation (APACHE) II score, and higher level of care in the first 24 h of ICU admission. Additional predictors for withholding included being of Chinese race, the religions of Hinduism and Islam, malignancy, and chronic liver failure. The additional predictor for withdrawal was lower hospital paying class (with greater government subsidy for hospital bills). Hospital mortality in patients without LST limitation, with LST withholding, and with LST withdrawal was 10.6%, 82.1%, and 91.8%, respectively (p < 0.001). Withholding (odds ratio 13.822, 95% confidence interval 9.987-19.132) and withdrawal (odds ratio 38.319, 95% confidence interval 24.351-60.298) were both found to be independent predictors of hospital mortality on multivariable analysis. CONCLUSIONS Differences in the independent predictors of withholding and withdrawal of LST exist. Even after accounting for baseline characteristics, both withholding and withdrawal of LST independently predict hospital mortality. Later mortality in patients who had LST withdrawn compared to withholding suggests that the decision to withdraw may be at the point when medical futility is recognised.
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Affiliation(s)
- Clare Fong
- FAST and Chronic Programmes, Alexandra Hospital, 378 Alexandra Road, Singapore, 159964, Singapore.
- Division of Respiratory and Critical Care Medicine, Department of Medicine, National University Hospital, 1E Kent Ridge Road, Singapore, 119228, Singapore.
| | - Wern Lunn Kueh
- Division of Respiratory and Critical Care Medicine, Department of Medicine, National University Hospital, 1E Kent Ridge Road, Singapore, 119228, Singapore
| | - Sennen Jin Wen Lew
- Department of Respiratory and Critical Care Medicine, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore, 308433, Singapore
| | - Benjamin Choon Heng Ho
- Department of Respiratory and Critical Care Medicine, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore, 308433, Singapore
| | - Yu-Lin Wong
- Department of Anaesthesiology, Intensive Care and Pain Medicine, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore, 308433, Singapore
| | - Yie Hui Lau
- Department of Anaesthesiology, Intensive Care and Pain Medicine, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore, 308433, Singapore
| | - Yew Woon Chia
- Cardiac Intensive Care Unit, Department of Cardiology, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore, 308433, Singapore
| | - Hui Ling Tan
- Department of Anaesthesiology, Intensive Care and Pain Medicine, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore, 308433, Singapore
| | - Ying Hao Christopher Seet
- Department of Neurology, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore, 308433, Singapore
| | - Wen Ting Siow
- FAST and Chronic Programmes, Alexandra Hospital, 378 Alexandra Road, Singapore, 159964, Singapore
- Division of Respiratory and Critical Care Medicine, Department of Medicine, National University Hospital, 1E Kent Ridge Road, Singapore, 119228, Singapore
| | - Graeme MacLaren
- Cardiothoracic ICU, Department of Cardiac, Thoracic and Vascular Surgery, National University Heart Centre, 1E Kent Ridge Road, Singapore, 119228, Singapore
| | - Rohit Agrawal
- Department of Anaesthesia, National University Hospital, 5 Lower Kent Ridge Road, Singapore, 119074, Singapore
| | - Tian Jin Lim
- Department of Anaesthesia, National University Hospital, 5 Lower Kent Ridge Road, Singapore, 119074, Singapore
| | - Shir Lynn Lim
- Department of Cardiology, National University Heart Centre, 1E Kent Ridge Road, Singapore, 119228, Singapore
- Department of Medicine, National University of Singapore, 1E Kent Ridge Road, Singapore, 119228, Singapore
- Pre-Hospital and Emergency Research Center, Duke-NUS Medical School, 8 College Rd, Singapore, 16985, Singapore
| | - Toon Wei Lim
- Department of Cardiology, National University Heart Centre, 1E Kent Ridge Road, Singapore, 119228, Singapore
| | - Vui Kian Ho
- Department of Intensive Care Medicine, Sengkang General Hospital, 110 Sengkang East Way, Singapore, 544886, Singapore
- Department of Surgical Intensive Care, Singapore General Hospital, Outram Road, Singapore, 169608, Singapore
| | - Chai Rick Soh
- Department of Anaesthesiology, Singapore General Hospital, Outram Road, Singapore, 169608, Singapore
| | - Duu Wen Sewa
- Department of Respiratory and Critical Care Medicine, Singapore General Hospital, Outram Road, Singapore, 169608, Singapore
| | - Chian Min Loo
- Department of Respiratory and Critical Care Medicine, Singapore General Hospital, Outram Road, Singapore, 169608, Singapore
| | - Faheem Ahmed Khan
- Department of Intensive Care Medicine, Ng Teng Fong General Hospital, 1 Jurong East Street 21, Singapore, 609606, Singapore
| | - Chee Keat Tan
- Department of Intensive Care Medicine, Ng Teng Fong General Hospital, 1 Jurong East Street 21, Singapore, 609606, Singapore
| | - Roshni Sadashiv Gokhale
- Department of Intensive Care, Changi General Hospital, 2 Simei Street 3, Singapore, 529889, Singapore
| | - Chuin Siau
- Department of Respiratory and Critical Care Medicine, Changi General Hospital, 2 Simei Street 3, Singapore, 529889, Singapore
| | - Noelle Louise Siew Hua Lim
- Department of Anaesthesia and Surgical Intensive Care, Changi General Hospital, 2 Simei Street 3, Singapore, 529889, Singapore
| | - Chik-Foo Yim
- Department of Women's Anaesthesia, KK Women's and Children's Hospital, 100 Bukit Timah Road, Singapore, 229899, Singapore
| | - Jonathen Venkatachalam
- Department of Respiratory and Critical Care Medicine, Khoo Teck Puat Hospital, 90 Yishun Central, Singapore, 768828, Singapore
| | - Kumaresh Venkatesan
- Department of Anaesthesia, Khoo Teck Puat Hospital, 90 Yishun Central, Singapore, 768828, Singapore
| | - Naville Chi Hock Chia
- Department of Anaesthesia, Khoo Teck Puat Hospital, 90 Yishun Central, Singapore, 768828, Singapore
- Yong Loo Lin School of Medicine, 10 Medical Dr, Singapore, 117597, Singapore
- Lee Kong Chian School of Medicine, 11 Mandalay Rd, Singapore, 308232, Singapore
| | - Mei Fong Liew
- FAST and Chronic Programmes, Alexandra Hospital, 378 Alexandra Road, Singapore, 159964, Singapore
- Division of Respiratory and Critical Care Medicine, Department of Medicine, National University Hospital, 1E Kent Ridge Road, Singapore, 119228, Singapore
| | - Guihong Li
- Department of Intensive Care Unit Operations, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore, 308433, Singapore
| | - Li Li
- Department of Intensive Care Unit Operations, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore, 308433, Singapore
| | - Su Mon Myat
- Division of Respiratory and Critical Care Medicine, Department of Medicine, National University Hospital, 1E Kent Ridge Road, Singapore, 119228, Singapore
| | - Zena Zena
- Department of Respiratory and Critical Care Medicine, Singapore General Hospital, Outram Road, Singapore, 169608, Singapore
| | - Shuling Zhuo
- Department of Intensive Care Medicine, Ng Teng Fong General Hospital, 1 Jurong East Street 21, Singapore, 609606, Singapore
| | - Ling Ling Yueh
- Department of Intensive Care Medicine, Ng Teng Fong General Hospital, 1 Jurong East Street 21, Singapore, 609606, Singapore
| | - Caroline Shu Fang Tan
- Department of Intensive Care Medicine, Sengkang General Hospital, 110 Sengkang East Way, Singapore, 544886, Singapore
| | - Jing Ma
- Division of Nursing, KK Women's and Children's Hospital, 100 Bukit Timah Road, Singapore, 229899, Singapore
| | - Siew Lian Yeo
- Division of Nursing, KK Women's and Children's Hospital, 100 Bukit Timah Road, Singapore, 229899, Singapore
| | - Yiong Huak Chan
- Biostatistics Unit, Yong Loo Lin School of Medicine, National University of Singapore, 1E Kent Ridge Road, Singapore, 119228, Singapore
| | - Jason Phua
- FAST and Chronic Programmes, Alexandra Hospital, 378 Alexandra Road, Singapore, 159964, Singapore
- Division of Respiratory and Critical Care Medicine, Department of Medicine, National University Hospital, 1E Kent Ridge Road, Singapore, 119228, Singapore
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2
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Tee A, Choo BP, Gokhale RS, Wang X, Mansor M, Oh HC, Jones D. Findings from a decade of experience following implementation of a Rapid Response System into an Asian hospital. Resusc Plus 2023; 16:100461. [PMID: 37693336 PMCID: PMC10482888 DOI: 10.1016/j.resplu.2023.100461] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2023] [Revised: 08/05/2023] [Accepted: 08/17/2023] [Indexed: 09/12/2023] Open
Abstract
Aim Rapid response systems (RRS) are present in many acute hospitals in western nations but are not widely adopted in Asia. The influence of healthcare culture and the effect of implementing an RRS over time are infrequently reported. We describe the introduction a RRS into a Singaporean hospital and the barriers encountered. The efferent limb activation rates, cardiac arrest rates and unplanned intensive care unit (ICU) admissions are trended over eleven years. Methods We conducted a retrospective observational study using prospectively collected data derived from administrative and Medical Emergency Team (MET) databases. Results The RRS used a MET with a single parameter track and trigger and physician led efferent limb. Barriers encountered included clinical leadership buy-in, assembling and equipping the efferent team, maintaining a non-punitive mindset, improving accessibility to MET and communicating the impact of the MET. Over an 11-year period with 488,252 hospital admissions, MET activation rates increased from 1.6/1000 admissions (2009) to 14.1/1000 admissions (2019). Code blue activations and unplanned ICU admission rates decreased from 2.9 to 1.7 and from 8.8 to 2.0/1000 admissions, respectively over the 11 years. There were associations between increasing MET activation rate and reduction in code blue activations (p = 0.013) and unplanned medical ICU admission rates (p = 0.001). Conclusion Implementing, sustaining and continued improvement of an RRS in Singapore is possible despite challenges encountered. With increasing activation rates over a decade, there were reductions in cardiac arrest rates and unplanned medical ICU admissions.
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Affiliation(s)
- Augustine Tee
- Respiratory and Critical Care Medicine, Changi General Hospital, Singapore
| | | | | | - Xiqin Wang
- Advanced Practice Nurse Development, Changi General Hospital, Singapore
| | | | - Hong Choon Oh
- Health Services Research, Changi General Hospital, Singapore
| | - Daryl Jones
- Department of Intensive Care Unit, Austin Hospital, Australia
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3
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Gokhale RS, Wee I, Choo TP, See M, Chuin S. The use of protocolised sedation to reduce benzodiazepine use and improve sedation practices in a medical intensive care unit in Singapore. Singapore Med J 2023; 0:369367. [PMID: 36861621 DOI: 10.4103/singaporemedj.smj-2021-060] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
Affiliation(s)
| | - Ian Wee
- Department of Pharmacy, Changi General Hospital, Singapore
| | | | - Michelle See
- Department of Pharmacy, Changi General Hospital, Singapore
| | - Siau Chuin
- Respiratory and Critical Care Medicine, Changi General Hospital, Singapore
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4
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Sieow NYF, Goh JTK, Gokhale RS, Tan YH. Characteristics, risk factors and outcomes of critically ill patients with active TB. Int J Tuberc Lung Dis 2022; 26:537-543. [PMID: 35650699 DOI: 10.5588/ijtld.21.0723] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND: TB continues to impose a significant healthcare burden despite advancement in diagnostics and increased availability of effective antimicrobials. Recent years have seen a resurgence of the disease in association with increasing life expectancy and use of immunosuppressive therapy. Mortality remains high in TB patients requiring admission to critical care units.METHODS: We conducted a retrospective study in two public hospitals to determine factors associated with mortality in patients with TB requiring critical care admission. All patients aged ≥21 years with a diagnosis of active TB involving any organ system at the time of a critical care admission were eligible. The primary outcome measure was 30-day mortality.RESULTS: Over the study period of 4 years, 148 patients were identified. Overall 30-day mortality was 36.5%. Based on multivariate analysis, factors which independently correlated with 30-day mortality include higher APACHE II (Acute Physiology and Chronic Health Evaluation II) score, acid-fast bacilli smear positivity, initiation of anti-TB treatment prior to critical care admission and need for renal replacement therapy.CONCLUSION: TB in critically ill patients continues to be associated with significant mortality. The factors identified to be associated with poor survival outcomes in our study were largely related to greater disease burden and potential for suboptimal treatment.
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Affiliation(s)
- N Y F Sieow
- Department of Respiratory and Critical Care Medicine, Changi General Hospital, Singapore
| | - J T K Goh
- Department of Respiratory and Critical Care Medicine, Sengkang General Hospital, Singapore
| | - R S Gokhale
- Department of Internal Medicine, Changi General Hospital, Singapore
| | - Y H Tan
- Department of Respiratory and Critical Care Medicine, Singapore General Hospital, Singapore
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5
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Puah SH, Young BE, Chia PY, Ho VK, Loh J, Gokhale RS, Tan SY, Sewa DW, Kalimuddin S, Tan CK, Pada SKMS, Cove ME, Chai LYA, Parthasarathy P, Ho BCH, Ng JJ, Ling LM, Abisheganaden JA, Lee VJM, Tan CH, Lin RTP, Leo YS, Lye DC, Yeo TW. Clinical features and predictors of severity in COVID-19 patients with critical illness in Singapore. Sci Rep 2021; 11:7477. [PMID: 33820944 PMCID: PMC8021583 DOI: 10.1038/s41598-021-81377-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2020] [Accepted: 12/14/2020] [Indexed: 01/10/2023] Open
Abstract
We aim to describe a case series of critically and non-critically ill COVID-19 patients in Singapore. This was a multicentered prospective study with clinical and laboratory details. Details for fifty uncomplicated COVID-19 patients and ten who required mechanical ventilation were collected. We compared clinical features between the groups, assessed predictors of intubation, and described ventilatory management in ICU patients. Ventilated patients were significantly older, reported more dyspnea, had elevated C-reactive protein and lactate dehydrogenase. A multivariable logistic regression model identified respiratory rate (aOR 2.83, 95% CI 1.24–6.47) and neutrophil count (aOR 2.39, 95% CI 1.34–4.26) on admission as independent predictors of intubation with area under receiver operating characteristic curve of 0.928 (95% CI 0.828–0.979). Median APACHE II score was 19 (IQR 17–22) and PaO2/FiO2 ratio before intubation was 104 (IQR 89–129). Median peak FiO2 was 0.75 (IQR 0.6–1.0), positive end-expiratory pressure 12 (IQR 10–14) and plateau pressure 22 (IQR 18–26) in the first 24 h of ventilation. Median duration of ventilation was 6.5 days (IQR 5.5–13). There were no fatalities. Most COVID-19 patients in Singapore who required mechanical ventilation because of ARDS were extubated with no mortality.
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Affiliation(s)
| | - Barnaby Edward Young
- Tan Tock Seng Hospital, Singapore, Singapore.,National Centre for Infectious Diseases, Singapore, Singapore.,Lee Kong Chian School of Medicine, Novena Campus Clinical Sciences Building, 11 Mandalay Rd, Singapore, 308232, Singapore
| | - Po Ying Chia
- Tan Tock Seng Hospital, Singapore, Singapore.,National Centre for Infectious Diseases, Singapore, Singapore.,Lee Kong Chian School of Medicine, Novena Campus Clinical Sciences Building, 11 Mandalay Rd, Singapore, 308232, Singapore
| | - Vui Kian Ho
- Sengkang General Hospital, Singapore, Singapore
| | - Jiashen Loh
- Sengkang General Hospital, Singapore, Singapore
| | | | - Seow Yen Tan
- Singapore General Hospital, Singapore, Singapore
| | - Duu Wen Sewa
- Singapore General Hospital, Singapore, Singapore
| | - Shirin Kalimuddin
- Singapore General Hospital, Singapore, Singapore.,Duke-NUS Medical School, Singapore, Singapore
| | | | - Surinder K M S Pada
- Ng Teng Fong General Hospital, Singapore, Singapore.,Yong Loo Lin School of Medicine, Singapore, Singapore
| | - Matthew Edward Cove
- National University Hospital, Singapore, Singapore.,Yong Loo Lin School of Medicine, Singapore, Singapore
| | - Louis Yi Ann Chai
- National University Hospital, Singapore, Singapore.,Yong Loo Lin School of Medicine, Singapore, Singapore
| | | | | | | | - Li Min Ling
- Tan Tock Seng Hospital, Singapore, Singapore.,National Centre for Infectious Diseases, Singapore, Singapore.,Lee Kong Chian School of Medicine, Novena Campus Clinical Sciences Building, 11 Mandalay Rd, Singapore, 308232, Singapore
| | - John A Abisheganaden
- Tan Tock Seng Hospital, Singapore, Singapore.,Lee Kong Chian School of Medicine, Novena Campus Clinical Sciences Building, 11 Mandalay Rd, Singapore, 308232, Singapore
| | - Vernon J M Lee
- Ministry of Health, Singapore, Singapore.,Saw Swee Hock School of Public Health, Singapore, Singapore
| | - Cher Heng Tan
- Tan Tock Seng Hospital, Singapore, Singapore.,Lee Kong Chian School of Medicine, Novena Campus Clinical Sciences Building, 11 Mandalay Rd, Singapore, 308232, Singapore
| | - Raymond T P Lin
- National Centre for Infectious Diseases, Singapore, Singapore.,Yong Loo Lin School of Medicine, Singapore, Singapore
| | - Yee Sin Leo
- Tan Tock Seng Hospital, Singapore, Singapore.,National Centre for Infectious Diseases, Singapore, Singapore.,Lee Kong Chian School of Medicine, Novena Campus Clinical Sciences Building, 11 Mandalay Rd, Singapore, 308232, Singapore.,Yong Loo Lin School of Medicine, Singapore, Singapore.,Saw Swee Hock School of Public Health, Singapore, Singapore
| | - David C Lye
- Tan Tock Seng Hospital, Singapore, Singapore.,National Centre for Infectious Diseases, Singapore, Singapore.,Lee Kong Chian School of Medicine, Novena Campus Clinical Sciences Building, 11 Mandalay Rd, Singapore, 308232, Singapore.,Yong Loo Lin School of Medicine, Singapore, Singapore
| | - Tsin Wen Yeo
- Tan Tock Seng Hospital, Singapore, Singapore. .,National Centre for Infectious Diseases, Singapore, Singapore. .,Lee Kong Chian School of Medicine, Novena Campus Clinical Sciences Building, 11 Mandalay Rd, Singapore, 308232, Singapore. .,Menzies School of Health Research, Charles Darwin University, Darwin, Australia.
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6
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Wong YJ, Chew SY, Hsiang JC, Thurairajah PH, Kumar R, Teo EK, Gokhale RS, Noor IBM, Tan J. VIEKIRA PAK associated drug-induced interstitial lung disease: Case series with systematic review of literature. Clin Mol Hepatol 2018; 25:218-222. [PMID: 30184617 PMCID: PMC6589856 DOI: 10.3350/cmh.2018.0017] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Accepted: 07/13/2018] [Indexed: 02/05/2023] Open
Affiliation(s)
- Yu Jun Wong
- Department of Gastroenterology and Hepatology, Changi General Hospital, Singapore
| | - Si Yuan Chew
- Department of Respiratory Medicine and Critical Care, Changi General Hospital, Singapore, Singapore
| | - John Chen Hsiang
- Department of Gastroenterology and Hepatology, Changi General Hospital, Singapore
| | | | - Rahul Kumar
- Department of Gastroenterology and Hepatology, Changi General Hospital, Singapore
| | - Eng Kiong Teo
- Department of Gastroenterology and Hepatology, Changi General Hospital, Singapore
| | - Roshni Sadashiv Gokhale
- Department of Respiratory Medicine and Critical Care, Changi General Hospital, Singapore, Singapore
| | - Imran Bin Mohamed Noor
- Department of Respiratory Medicine and Critical Care, Changi General Hospital, Singapore, Singapore
| | - Jessica Tan
- Department of Gastroenterology and Hepatology, Changi General Hospital, Singapore
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7
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Dani P, Patnaik N, Singh A, Jaiswal A, Agrawal B, Kumar AA, Varkhande SR, Sharma A, Vaish U, Ghosh P, Sharma VK, Sharma P, Verma G, Kar HK, Gupta S, Natarajan VT, Gokhale RS, Rani R. Association and expression of the antigen-processing gene PSMB8, coding for low-molecular-mass protease 7, with vitiligo in North India: case-control study. Br J Dermatol 2017; 178:482-491. [PMID: 28207947 DOI: 10.1111/bjd.15391] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/13/2017] [Indexed: 12/19/2022]
Abstract
BACKGROUND Vitiligo is a multifactorial, autoimmune, depigmenting disorder of the skin where aberrant presentation of autoantigens may have a role. OBJECTIVES To study the association of two antigen-processing genes, PSMB8 and PSMB9, with vitiligo. METHODS In total 1320 cases of vitiligo (1050 generalized and 270 localized) and 752 healthy controls were studied for the PSMB9 exon 3 G/A single-nucleotide polymorphism (SNP), PSMB8 exon 2 C/A SNP and PSMB8 intron 6 G/T SNP at site 37 360 using polymerase chain reaction (PCR)-restriction fragment length polymorphism. Real-time PCR was used for transcriptional expression of PSMB8 and cytokines. Expression of ubiquitinated proteins and phosphorylated-p38 (P-p38) was studied by Western blotting. RESULTS Significant increases in PSMB8 exon 2 allele A (P < 2.07 × 10-6 , odds ratio 1·93) and genotypes AA (P < 1.03 × 10-6 , odds ratio 2·51) and AC (P < 1.29 × 10-6 , odds ratio 1·63) were observed in patients with vitiligo. Interferon-γ stimulation induced lower expression of PSMB8 in peripheral blood mononuclear cells of cases compared with controls, suggesting impaired antigen processing, which was confirmed by accumulation of ubiquitinated proteins in both lesional and nonlesional skin of patients with vitiligo. Expression of proinflammatory cytokines - interleukin (IL)-6, IL-1β and IL-8 - was higher in the lesional skin. P-p38 expression was variable but correlated with the amount of ubiquitinated proteins in the lesional and nonlesional skin, suggesting that the inflammatory cytokine responses in lesional skin could be a result of both P-p38-dependent and -independent pathways. CONCLUSIONS The PSMB8 exon 2 SNP is significantly associated with vitiligo. Accumulation of ubiquitinated proteins in skin of cases of vitiligo suggests their aberrant processing, which may promote the development of the disease.
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Affiliation(s)
- P Dani
- Molecular Immunogenetics Group, National Institute of Immunology, New Delhi, 110067, India
| | - N Patnaik
- Molecular Immunogenetics Group, National Institute of Immunology, New Delhi, 110067, India
| | - A Singh
- Molecular Immunogenetics Group, National Institute of Immunology, New Delhi, 110067, India.,Systems Biology Group, CSIR - Institute of Genomics and Integrative Biology, New Delhi, 110025, India
| | - A Jaiswal
- Molecular Immunogenetics Group, National Institute of Immunology, New Delhi, 110067, India
| | - B Agrawal
- Molecular Immunogenetics Group, National Institute of Immunology, New Delhi, 110067, India
| | - A A Kumar
- Molecular Immunogenetics Group, National Institute of Immunology, New Delhi, 110067, India
| | - S R Varkhande
- Molecular Immunogenetics Group, National Institute of Immunology, New Delhi, 110067, India
| | - A Sharma
- Molecular Immunogenetics Group, National Institute of Immunology, New Delhi, 110067, India
| | - U Vaish
- Molecular Immunogenetics Group, National Institute of Immunology, New Delhi, 110067, India
| | - P Ghosh
- Systems Biology Group, CSIR - Institute of Genomics and Integrative Biology, New Delhi, 110025, India
| | - V K Sharma
- Department of Dermatology, All India Institute of Medical Sciences, New Delhi, 110029, India
| | - P Sharma
- Department of Dermatology, PGIMER, Dr Ram Manohar Lohia Hospital, New Delhi, 110001, India
| | - G Verma
- Department of Dermatology, PGIMER, Dr Ram Manohar Lohia Hospital, New Delhi, 110001, India
| | - H K Kar
- Department of Dermatology, PGIMER, Dr Ram Manohar Lohia Hospital, New Delhi, 110001, India
| | - S Gupta
- Department of Dermatology, All India Institute of Medical Sciences, New Delhi, 110029, India
| | - V T Natarajan
- Systems Biology Group, CSIR - Institute of Genomics and Integrative Biology, New Delhi, 110025, India
| | - R S Gokhale
- Molecular Immunogenetics Group, National Institute of Immunology, New Delhi, 110067, India.,Systems Biology Group, CSIR - Institute of Genomics and Integrative Biology, New Delhi, 110025, India
| | - R Rani
- Molecular Immunogenetics Group, National Institute of Immunology, New Delhi, 110067, India.,Systems Biology Group, CSIR - Institute of Genomics and Integrative Biology, New Delhi, 110025, India
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8
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Imran M, Laddha NC, Dwivedi M, Mansuri MS, Singh J, Rani R, Gokhale RS, Sharma VK, Marfatia YS, Begum R. Interleukin-4 genetic variants correlate with its transcript and protein levels in patients with vitiligo. Br J Dermatol 2012; 167:314-23. [PMID: 22512783 DOI: 10.1111/j.1365-2133.2012.11000.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
BACKGROUND Vitiligo is an acquired pigmentary disorder resulting from loss of melanocytes. Interleukin (IL)-4 has been shown to stimulate B-cell proliferation, to regulate immunoglobulin class switching (IgG1 and IgE) and to promote T-cell development. Polymorphisms in the IL4 gene are known to increase its expression, thereby implicating its role in vitiligo susceptibility. OBJECTIVES To explore intron 3 VNTR (IVS3) and -590 C/T (rs2243250) promoter polymorphisms in the IL4 gene and to correlate them with the IL4 transcript, serum IL-4 and IgE levels to achieve genotype-phenotype correlation in patients with vitiligo from Gujarat. A replication study was done in a North Indian population. METHODS The case-control study was performed to investigate these polymorphisms in 505 patients and 744 controls in Gujarat, and 596 patients and 397 controls in North India by polymerase chain reaction (PCR) and PCR-restriction fragment length polymorphism analysis. IL4 transcript levels were monitored by real-time PCR. Serum IL-4 and IgE levels were measured by enzyme-linked immunosorbent assay and electrochemiluminescence immunoassay, respectively. RESULTS The genotype frequencies differed significantly between patients with generalized vitiligo and controls for both the polymorphisms in both populations. Allele frequencies significantly differed between patients with generalized vitiligo and controls for both the polymorphisms in the population from Gujarat. Interestingly, genotype and allele frequencies for -590 C/T single nucleotide polymorphism were significantly different between patients with localized vitiligo and controls in both the populations. The study revealed significantly increased IL4 mRNA, serum IL-4 and IgE levels in patients from Gujarat. Age of onset analysis of disease in patients suggested that the TTR2R2, TTR1R2 and CTR2R2 haplotypes had a profound effect in the early onset of the disease. CONCLUSIONS Our results suggest that these polymorphisms of the IL4 gene may be genetic risk factors for susceptibility towards vitiligo and the upregulation of the IL4 transcript, protein and IgE levels in individuals with susceptible haplotypes reveal the crucial role of IL-4 in the pathogenesis of vitiligo.
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Affiliation(s)
- M Imran
- Department of Biochemistry, Faculty of Science, The Maharaja Sayajirao University of Baroda, Vadodara, Gujarat 390002, India
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9
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Abstract
Polyketide synthases catalyze the assembly of complex natural products from simple precursors such as propionyl-CoA and methylmalonyl-CoA in a biosynthetic process that closely parallels fatty acid biosynthesis. Like fatty acids, polyketides are assembled by successive decarboxylative condensations of simple precursors. But whereas the intermediates in fatty acid biosynthesis are fully reduced to generate unfunctionalized alkyl chains, the intermediates in polyketide biosynthesis may be only partially processed, giving rise to complex patterns of functional groups. Additional complexity arises from the use of different starter and chain extension substrates, the generation of chiral centers, and further functional group modifications, such as cyclizations. The structural and functional modularity of these multienzyme systems has raised the possibility that polyketide biosynthetic pathways might be rationally reprogrammed by combinatorial manipulation. An essential prerequisite for harnessing this biosynthetic potential is a better understanding of the molecular recognition features of polyketide synthases. Within this decade, a variety of genetic, biochemical, and chemical investigations have yielded insights into the tolerance and specificity of several architecturally different polyketide synthases. The results of these studies, together with their implications for biosynthetic engineering, are summarized in this review.
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Affiliation(s)
- C Khosla
- Department of Chemical Engineering, Stanford University, California 94305-5025, USA.
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10
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Abstract
Multidomain proteins are common in a variety of cellular processes. Their domains are interconnected through short stretches of amino acid residues referred to as linkers. Recent studies on many systems have provided compelling evidence that linkers are more than simple covalent connectors. They also perform the important task of establishing communication between the different functional modules that exist within such proteins.
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Affiliation(s)
- R S Gokhale
- Department of Chemical Engineering, Stanford University, Stanford, CA 94305-5025, USA.
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11
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Abstract
Modular polyketide synthases catalyze the biosynthesis of medicinally important natural products through an assembly-line mechanism. Although these megasynthases display very precise overall selectivity, we show that their constituent modules are remarkably tolerant toward diverse incoming acyl chains. By appropriate engineering of linkers, which exist within and between polypeptides, it is possible to exploit this tolerance to facilitate the transfer of biosynthetic intermediates between unnaturally linked modules. This protein engineering strategy also provides insights into the evolution of modular polyketide synthases.
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Affiliation(s)
- R S Gokhale
- Department of Chemical Engineering, Stanford University, Stanford CA 94305-5025, USA
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12
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Velanker SS, Gokhale RS, Ray SS, Gopal B, Parthasarathy S, Santi DV, Balaram P, Murthy MR. Disulfide engineering at the dimer interface of Lactobacillus casei thymidylate synthase: crystal structure of the T155C/E188C/C244T mutant. Protein Sci 1999; 8:930-3. [PMID: 10211840 PMCID: PMC2144305 DOI: 10.1110/ps.8.4.930] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
The crystal structure of a covalently cross-linked Lactobacillus casei thymidylate synthase has been determined at 2.8 A resolution. The sites for mutation to achieve the bis-disulfide linked dimer were identified using the disulfide modeling program MODIP. The mutant so obtained was found to be remarkably thermostable. This increase in stability has been reasoned to be entirely a consequence of the covalent gluing between the two subunits.
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Affiliation(s)
- S S Velanker
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore
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13
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Gokhale RS, Hunziker D, Cane DE, Khosla C. Mechanism and specificity of the terminal thioesterase domain from the erythromycin polyketide synthase. Chem Biol 1999; 6:117-25. [PMID: 10021418 DOI: 10.1016/s1074-5521(99)80008-8] [Citation(s) in RCA: 127] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
BACKGROUND Polyketides are important compounds with antibiotic and anticancer activities. Several modular polyketide synthases (PKSs) contain a terminal thioesterase (TE) domain probably responsible for the release and concomitant cyclization of the fully processed polyketide chain. Because the TE domain influences qualitative aspects of product formation by engineered PKSs, its mechanism and specificity are of considerable interest. RESULTS The TE domain of the 6-deoxyerythronolide B synthase was overexpressed in Escherichia coli. When tested against a set of N-acetyl cysteamine thioesters the TE domain did not act as a cyclase, but showed significant hydrolytic specificity towards substrates that mimic important features of its natural substrate. Also the overall rate of polyketide chain release was strongly enhanced by a covalent connection between the TE domain and the terminal PKS module (by as much as 100-fold compared with separate TE and PKS 'domains'). CONCLUSIONS The inability of the TE domain alone to catalyze cyclization suggests that macrocycle formation results from the combined action of the TE domain and a PKS module. The chain-length and stereochemical preferences of the TE domain might be relevant in the design and engineered biosynthesis of certain novel polyketides. Our results also suggest that the TE domain might loop back to catalyze the release of polyketide chains from both terminal and pre-terminal modules, which may explain the ability of certain naturally occurring PKSs, such as the picromycin synthase, to generate both 12-membered and 14-membered macrolide antibiotics.
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Affiliation(s)
- R S Gokhale
- Department of Chemical Engineering, Stanford University, CA 94305-5025,USA
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14
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Gokhale RS, Ray SS, Balaram H, Balaram P. Unfolding of Plasmodium falciparum triosephosphate isomerase in urea and guanidinium chloride: evidence for a novel disulfide exchange reaction in a covalently cross-linked mutant. Biochemistry 1999; 38:423-31. [PMID: 9890925 DOI: 10.1021/bi981087s] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The conformational stability of Plasmodium falciparum triosephosphate isomerase (TIMWT) enzyme has been investigated in urea and guanidinium chloride (GdmCl) solutions using circular dichroism, fluorescence, and size-exclusion chromatography. The dimeric enzyme is remarkably stable in urea solutions. It retains considerable secondary, tertiary, and quaternary structure even in 8 M urea. In contrast, the unfolding transition is complete by 2.4 M GdmCl. Although the secondary as well as the tertiary interactions melt before the perturbation of the quaternary structure, these studies imply that the dissociation of the dimer into monomers ultimately leads to the collapse of the structure, suggesting that the interfacial interactions play a major role in determining multimeric protein stability. The Cm(urea)/Cm(GdmCl) ratio (where Cm is the concentration of the denaturant required at the transition midpoint) is unusually high for triosephosphate isomerase as compared to other monomeric and dimeric proteins. A disulfide cross-linked mutant protein (Y74C) engineered to form two disulfide cross-links across the interface (13-74') and (13'-74) is dramatically destablized in urea. The unfolding transition is complete by 6 M urea and involves a novel mechanism of dimer dissociation through intramolecular thiol-disulfide exchange.
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Affiliation(s)
- R S Gokhale
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore
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15
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Gopal B, Ray SS, Gokhale RS, Balaram H, Murthy MR, Balaram P. Cavity-creating mutation at the dimer interface of Plasmodium falciparum triosephosphate isomerase: restoration of stability by disulfide cross-linking of subunits. Biochemistry 1999; 38:478-86. [PMID: 9890931 DOI: 10.1021/bi981495w] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Disulfide engineering across subunit interfaces provides a means of inhibiting dissociation during unfolding of multimeric enzymes. Two symmetry-related intersubunit disulfide bridges were introduced across the interface of the dimeric enzyme triosephosphate isomerase from Plasmodium falciparum. This was achieved by mutating a tyrosine residue at position 74 at the subunit interface to a cysteine, thereby enabling it to form a covalent cross-link with a pre-existing cysteine at position 13 of the other subunit. The wild-type enzyme (TIMWT) and the oxidized (Y74Cox) and reduced (Y74Cred) forms of the mutant have similar enzymatic activity, absorption, and fluorescence spectra. All three proteins have similar far-UV CD spectra. The Y74Cred shows a distinct loss of near-UV CD. Thermal precipitation studies demonstrate that TIMWT and Y74Cox have very similar Tm values (Tm approximately 60 degreesC) whereas Y74Cred is surprisingly labile (Tm approximately 38 degreesC). The Y74C mutant results in the creation of a large cavity (approximately 100 A3) at the dimer interface. The crystal structure for the oxidized form of Y74C mutant, crystallized in the presence of low concentrations of dithiothreitol, reveals an asymmetric dimer containing a disulfide bridge at one site and a reduced dithiol cysteine at the other. The crystal structure of the mutant offers insights into the destabilization effects of the interfacial cavities and the role of disulfide tethering in restoring protein stability.
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Affiliation(s)
- B Gopal
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore
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16
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Gokhale RS, Lau J, Cane DE, Khosla C. Functional orientation of the acyltransferase domain in a module of the erythromycin polyketide synthase. Biochemistry 1998; 37:2524-8. [PMID: 9485401 DOI: 10.1021/bi971887n] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Modular polyketide synthases (PKSs), such as the 6-deoxyerythronolide B synthase (DEBS), catalyze the biosynthesis of structurally complex and medicinally important natural products. These large multienzymes are organized into a series of functional units known as modules. Each dimeric module contains two catalytically independent clusters of active sites homologous to those of vertebrate fatty acid synthases. Earlier studies have shown that modules consist of head-to-tail homodimers in which ketosynthase (KS) and acyl carrier protein (ACP) domains are contributed by opposite subunits to form a catalytic center. Here, we probe the functional topology of the acyltransferase (AT) domain which transfers the methylmalonyl moiety of methylmalonyl-CoA onto the phosphopantetheine arm of the ACP domain. Using a bimodular derivative of DEBS, the AT domain of module 2 (AT2) was inactivated by site-directed mutagenesis. Heterodimeric protein pairs were generated in vitro between the inactivated AT2 (AT2 degrees) polypeptide and an inactive KS1 (KS1 degrees) or KS2 (KS2 degrees) protein. Both of these hybrid proteins supported polyketide synthesis, suggesting that AT2 can perform its function from either subunit. The apparent catalytic rate constants for each of the two hybrid protein pairs, KS1 degrees/AT2 degrees and KS2 degrees/AT2 degrees, were identical, indicating that no significant kinetic preference exists for a particular AT2-ACP2 combination. These results suggest that the AT domain can be shared between the two clusters of active sites within the same dimeric module. Such a novel structural organization might provide a functional advantage for the efficient biosynthesis of polyketides.
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Affiliation(s)
- R S Gokhale
- Department of Chemical Engineering, Chemistry, and Biochemistry, Stanford University, Stanford California 94305-5025, USA
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17
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Velanker SS, Ray SS, Gokhale RS, Suma S, Balaram H, Balaram P, Murthy MR. Triosephosphate isomerase from Plasmodium falciparum: the crystal structure provides insights into antimalarial drug design. Structure 1997; 5:751-61. [PMID: 9261072 DOI: 10.1016/s0969-2126(97)00230-x] [Citation(s) in RCA: 109] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
BACKGROUND Malaria caused by the parasite Plasmodium falciparum is a major public health concern. The parasite lacks a functional tricarboxylic acid cycle, making glycolysis its sole energy source. Although parasite enzymes have been considered as potential antimalarial drug targets, little is known about their structural biology. Here we report the crystal structure of triosephosphate isomerase (TIM) from P. falciparum at 2.2 A resolution. RESULTS The crystal structure of P. falciparum TIM (PfTIM), expressed in Escherichia coli, was determined by the molecular replacement method using the structure of trypanosomal TIM as the starting model. Comparison of the PfTIM structure with other TIM structures, particularly human TIM, revealed several differences. In most TIMs the residue at position 183 is a glutamate but in PfTIM it is a leucine. This leucine residue is completely exposed and together with the surrounding positively charged patch, may be responsible for binding TIM to the erythrocyte membrane. Another interesting feature is the occurrence of a cysteine residue at the dimer interface of PfTIM (Cys13), in contrast to human TIM where this residue is a methionine. Finally, residue 96 of human TIM (Ser96), which occurs near the active site, has been replaced by phenylalanine in PfTIM. CONCLUSIONS Although the human and Plasmodium enzymes share 42% amino acid sequence identity, several key differences suggest that PfTIM may turn out to be a potential drug target. We have identified a region which may be responsible for binding PfTIM to cytoskeletal elements or the band 3 protein of erythrocytes; attachment to the erythrocyte membrane may subsequently lead to the extracellular exposure of parts of the protein. This feature may be important in view of a recent report that patients suffering from P. falciparum malaria mount an antibody response to TIM leading to prolonged hemolysis. A second approach to drug design may be provided by the mutation of the largely conserved residue (Ser96) to phenylalanine in PfTIM. This difference may be of importance in designing specific active-site inhibitors against the enzyme. Finally, specific inhibition of PfTIM subunit assembly might be possible by targeting Cys13 at the dimer interface. The crystal structure of PfTIM provides a framework for new therapeutic leads.
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Affiliation(s)
- S S Velanker
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
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18
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Pieper R, Gokhale RS, Luo G, Cane DE, Khosla C. Purification and characterization of bimodular and trimodular derivatives of the erythromycin polyketide synthase. Biochemistry 1997; 36:1846-51. [PMID: 9048569 DOI: 10.1021/bi962324z] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Modular polyketide synthases (PKSs), such as the 6-deoxyerythronolide B synthase (DEBS), catalyze the biosynthesis of structurally complex and medicinally important natural products. DEBS is a dimeric protein complex that consists of three large multidomain polypeptide chains, DEBS 1, DEBS 2, and DEBS 3. In turn, each polypeptide includes two modules, where one module is responsible for a single round of condensation and associated reduction reactions. A hybrid protein comprised of the first two modules of DEBS fused to a thioesterase domain (DEBS 1 + TE) was purified to homogeneity in a fully active form (Kcat = 4.8 min-1). Synthesis of the anticipated triketide lactone required the presence of (2RS)-methylmalonyl-CoA and NADPH. When available, propionyl-CoA is the preferred source of primer units. However, in its absence the enzyme can derive primer units via decarboxylation of a methylmalonyl extender. The two subunits of an engineered trimodular derivative of DEBS, DEBS 1 and module 3 of DEBS 2 linked to the TE domain (module 3 + TE), were also individually purified and reconstituted to produce the expected tetraketide lactone in vitro (Kcat = 0.23 min-1). The considerably lower specific activity of this trimodular PKS relative to its bimodular counterpart presumably reflects inefficient association between DEBS 1 and module 3 + TE. As expected, module 3 + TE could be efficiently cross-linked as a homodimer. In contrast, no cross-links were detectable between modules 2 and 3, even though biosynthesis of the tetraketide requires transient interactions to occur between these two modules. Since module 3 only contains the minimal set of active sites required in a module (a ketosynthase, an acyltransferase, and an acyl carrier protein domain) and is the first active unimodular protein to be purified to homogeneity, it represents an attractive target for future biophysical and structural studies.
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Affiliation(s)
- R Pieper
- Department of Chemical Engineering, Stanford University, California 94305-5025, USA
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19
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Gokhale RS, Agarwalla S, Santi DV, Balaram P. Covalent reinforcement of a fragile region in the dimeric enzyme thymidylate synthase stabilizes the protein against chaotrope-induced unfolding. Biochemistry 1996; 35:7150-8. [PMID: 8679542 DOI: 10.1021/bi952890e] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Urea and guanidinium chloride induced unfolding of thymidylate synthase, a dimeric enzyme, and engineered interface mutants have been monitored by circular dichroism, fluorescence, and size-exclusion chromatography. Equilibrium unfolding studies show biphasic transitions, with a plateau between 3.5 and 5 M urea, when monitored by far-UV CD and fluorescence energy transfer employing an (aminoethylamino) naphthalenesulfonyl (AEDANS) label at the active site residue, Cys198. AEDANS was also specifically incorporated at position Cys155 in the mutant protein T155C. Direct excitation of this extrinsic fluorophore in the wild type protein (labeled at Cys198) and mutant T155C (labeled at Cys155) showed remarkable differences in the unfolding profiles. C155 AEDANS has a transition centered at 3.5 M urea, which is in contrast to Cys 198 AEDANS (5.5 M urea). Unfolding studies monitored by following intrinsic fluorescence of Trp residues which are located in a small structural domain suggest that this region of the protein is intrinsically fragile. The stable equilibrium intermediate is identified to be an ensemble of partially unfolded aggregated species by gel filtration studies. The chaotrope-induced denaturation of TS appears to proceed through a partially unfolded intermediate that is stabilized by aggregation. Dissociation and loss of structure occur concomitantly at high denaturant concentrations. Introduction of two symmetrically positioned disulfide bridges across the dimer interface in the triple mutant T155C/E188C/C244T (TSMox) stabilized the protein against denaturant-induced unfolding. Aggregate formation was completely abolished in the mutant TSMox, which also enhanced the overall structural stability of the protein. Structural reinforcement of the fragile interface in thymidylate synthase results in dramatic stabilization toward chaotrope-induced unfolding.
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Affiliation(s)
- R S Gokhale
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
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20
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Abstract
Thymidylate synthase (TS), a dimeric enzyme, forms large soluble aggregates at concentrations of urea (3.3-5M), well below that required for complete denaturation, as established by fluorescence and size-exclusion chromatography. In contrast to the wild-type enzyme, an engineered mutant of TS (T155C/E188C/C244T), TSMox, in which two subunits are crosslinked by disulfide bridges between residues 155-188' and 188-155' does not show this behavior. Aggregation behavior is restored upon disulfide bond reduction in the mutant protein, indicating the involvement of interface segments in forming soluble associated species. Intermolecular disulfide crosslinking has been used as a probe to investigate the formation of larger non-native aggregates. The studies argue for the formation of large multimeric species via a sticky patch of polypeptide from the dimer interface region that becomes exposed on partial unfolding. Covalent reinforcement of relatively fragile protein-protein interfaces may be a useful strategy in minimizing aggregation of non-native structures in multimeric proteins.
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Affiliation(s)
- S Agarwalla
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
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21
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Gokhale RS, Agarwalla S, Francis VS, Santi DV, Balaram P. Thermal stabilization of thymidylate synthase by engineering two disulfide bridges across the dimer interface. J Mol Biol 1994; 235:89-94. [PMID: 7904654 DOI: 10.1016/s0022-2836(05)80018-x] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Thermal inactivation of oligomeric enzymes is most often irreversible and is frequently accompanied by precipitation. We have engineered two symmetry related disulfide bridges (155-188' and 188-155') across the subunit interface of Lactobacillus casei thymidylate synthase, at sites chosen on the basis of an algorithm for the introduction of stereochemically unstrained bridges into proteins. In this communication, we demonstrate a remarkable enhancement in the thermal stability of the covalently cross-linked double disulfide containing dimeric enzyme. The mutant enzyme remains soluble and retains secondary structure even at 90 degrees C, in contrast to the wild-type enzyme which precipitates at 52 degrees C. Furthermore, the mutant enzyme has a temperature optimum of 55 degrees C and possesses appreciable enzymatic activity at 65 degrees C. Cooling restores complete activity, in the mutant protein, demonstrating reversible thermal unfolding. The results suggest that inter-subunit crosslinks can impart appreciable thermal stability in multimeric enzymes.
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Affiliation(s)
- R S Gokhale
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore
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22
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Punekar NS, Gokhale RS. Factors influencing the stability of heme and ferrochelatase: role of oxygen. Biotechnol Appl Biochem 1991; 14:21-9. [PMID: 1910584] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Ferrochelatase (EC 4.99.1.1) catalyzed heme synthesis is best accomplished in an anaerobic environment. Factors responsible for this phenomenon are not fully understood. Oxygen sensitivity of this reaction may be due to (a) oxidation of essential thiol groups on the enzyme, (b) oxidation of ferrous ions, or (c) the formation of hydrogen peroxide. These possibilities were investigated using rat liver ferrochelatase preparations and a continuous, dual-wavelength assay. Dithiothreitol and ascorbic acid stimulated the ferrochelatase reaction whereas GSH was not as effective. Addition of GSSG had little influence on the enzyme reaction. Total ferrochelatase activity in the assay remained unaffected at the end of the incubation and inclusion of glutathione peroxidase did not alter these results. Thus, ferrochelatase itself was not inactivated by oxidation. In selenium-deficient rats, the mitochondrial ferrochelatase levels were maintained even when glutathione peroxidase activity was significantly depleted. However, glutathione peroxidase very effectively inhibited the thiol-dependent aerobic degradation of heme. These results suggested that autoxidation of heme and of ferrous ions to the unusable ferric form largely contribute toward the oxygen sensitivity of the ferrochelatase reaction in vitro.
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Affiliation(s)
- N S Punekar
- Chemistry Department, Indian Institute of Technology, Powai, Bombay
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