How We Do It: Creating Consistent Structure and Content in Abdominal Radiology Report Templates.

OBJECTIVE: The purposes of this article are to describe the creation of template report formats and content for a variety of abdominal and pelvic CT and MRI examinations and discuss a review-of-systems approach to text and avoidance of pitfalls of report templates. CONCLUSION: Organ system-specific report templates for CT and MRI incorporate radiologist preferences. Disease-specific report templates are created from these reports to provide a consistent radiologist and referring physician experience across the report templates.

SYNTHESIS AND BIOLOGICAL EFFICACY OF NOVEL PIPERAZINE ANALOGUES BEARING QUINOLINE AND PYRIDINE MOIETIES.

A series of novel piperazine analogues bearing quinolin-8-yloxy-butan--ones/pyridin-2-yloxy-ethanones were synthesized by a simple and convenient approach based on various substituted piperazine incorporating quinoline and pyridine moieties. The analogues were evaluated for in vitro antioxidant activity against 2,2-diphenyl-1-picryl-hydrazyl (DPPH) and ferrous ion radical scavenging activities and anti-inflammatory activity by inhibition of Vipera russelli venom (PLA2) and gastric K+/H(+)-ATPase activities. Most of the title compounds exhibited promising activity. Best antioxidant and PLA2-inhibiting activities were found for piperazine analogues with phenyl and nitro phenyl groups, whereas methoxy group on phenyl piperazine indicated selectivity for the H+/K(+)-ATPase.

Synthesis, characterization, biological and catalytic applications of transition metal complexes derived from Schiff base.

A novel series of Cu(II), Ni(II), Zn(II), Co(II), and Cd(II) complexes have been synthesized from the Schiff base. Structural features were determined by analytical and spectral techniques like IR, (1)H NMR, UV-vis, elemental analysis, molar electric conductibility, magnetic susceptibility and thermal studies. The complexes are found to be soluble in dimethylformamide and dimethylsulfoxide. Molar conductance values in dimethylformamide indicate the non-electrolytic nature of the complexes. Binding of synthesized complexes with calf thymus DNA (CT DNA) was studied. There is significant binding of DNA in lanes 2, 3, and 5. Lanes 4 and 6 are showing more florescence when compared to the control indicating that these molecules are strongly bound to the DNA by inserting themselves between the two stacked base pairs and exhibiting their original property of fluorescence. Angiogenesis study has revealed that the compounds B-2, B-4 and B-5 have potent antitumor efficacy and activation of antiangiogenesis could be one of the possible underlying mechanisms of tumor inhibition.

Design, synthesis, and anticancer properties of novel benzophenone-conjugated coumarin analogs.

In the current scenario, development of anticancer drugs with specific targets is of prime importance in modern chemical biology. Observing the importance of benzophenone and coumarin nucleus, it would be worthwhile to design and synthesize novel benzophenone derivatives (8a-o) bearing the coumarin nucleus. Further, they were screened for prospective anticancer activities in vitro against the Michigan Cancer Foundation-7 (MCF-7) and Ehrlich's ascites tumor (EAT) cell lines and their biomarkers, followed by in silico studies regarding phosphoinositide 3-kinase (PI3K) and caspase by molecular docking. Benzophenones have been reported as potential drugs targeting tumor angiogenesis; thus, the formation of neovessels in an in vivo model system like CAM, which is angiogenesis dependent, was observed in the presence of compounds 8a-o. The above findings would help in understanding their putative potential as therapeutic agents for cancer patients.

An insight into the cytotoxic, antimicrobial, antioxidant, and biocontrol perspective of novel Iron(III) complexes of substituted benzimidazoles: Inhibition kinetics and molecular simulations.

Mononuclear complexes [FeCl3L2(OH2)] (L = L1, L2) were designed and synthesized by combining FeCl3 with 2-(3'-Aminophenylbenzimidazole) (L1) and 2-[(3'-N-Salicylidinephenyl)benzimidazole] (L2) and were characterized by physico-analytical strategies. The redox properties of the complexes were disclosed by the cyclic voltammetric method. Further, the interactions of complexes with proteins were studied by performing molecular docking engaging protein models of common cancer therapeutic targets to foresee their affinity to bind to these proteins. The complexes evidenced better protein-ligand docking (-8.4 and -9.0 kcal mol-1) and higher binding energies than their ligands. However, the L1 complex displayed improved binding free energy (-33.576 ± 1.01 kcal mol-1) compared to the other complexes and individual ligands. These compounds were screened for in vitro cytotoxic assays against triple-negative breast cancer cell lines (MDA-MB-468 cells), anti-inflammatory, antimicrobial, and antioxidant properties. The in vitro study complemented the in silico assay; therefore, these compounds may be a viable choice for expanding anticancer therapy. Additionally, the L2 showed better biocontrol activity owing to the enhanced growth of Trichoderma and inhibited the growth of Fusarium oxysporum.Communicated by Ramaswamy H. Sarma.

ACR Appropriateness Criteria® Adrenal Mass Evaluation: 2021 Update.

The appropriate evaluation of adrenal masses is strongly dependent on the clinical circumstances in which it is discovered. Adrenal incidentalomas are masses that are discovered on imaging studies that have been obtained for purposes other than adrenal disease. Although the vast majority of adrenal incidentalomas are benign, further radiological and biochemical evaluation of these lesions is important to arrive at a specific diagnosis. Patients with a history of malignancy or symptoms of excess hormone require different imaging evaluations than patients with incidentalomas. This document reviews imaging approaches to adrenal masses and the various modalities utilized in evaluation of adrenal lesions. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

ACR Appropriateness Criteria® Lower Urinary Tract Symptoms-Suspicion of Benign Prostatic Hyperplasia.

Lower urinary tract symptoms due to benign prostatic enlargement have a high prevalence in men over 50 years of age. Diagnosis is made with a combination of focused history and physician examination and validated symptom questionnaires. Urodynamic studies can help to differentiate storage from voiding abnormalities. Pelvic ultrasound may be indicated to assess bladder volume and wall thickness. Other imaging modalities, including prostate MRI, are usually not indicated in the initial workup and evaluation of uncomplicated lower urinary tract symptoms from an enlarged prostate. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

ACR Appropriateness Criteria® Penetrating Trauma-Lower Abdomen and Pelvis.

Lower urinary tract injury is most commonly the result of blunt trauma but can also result from penetrating or iatrogenic trauma. Clinical findings in patients with a mechanism of penetrating trauma to the lower urinary tract include lacerations or puncture wounds of the pelvis, perineum, buttocks, or genitalia, as well as gross hematuria or inability to void. CT cystography or fluoroscopy retrograde cystography are usually the most appropriate initial imaging procedures in patients with a mechanism of penetrating trauma to the lower urinary tract. CT of the pelvis with intravenous contrast, pelvic radiography, fluoroscopic retrograde urethrography, and CT of the pelvis without intravenous contrast may be appropriate in some cases. Arteriography, radiographic intravenous urography, CT of the pelvis without and with intravenous contrast, ultrasound, MRI, and nuclear scintigraphy are usually not appropriate. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

ACR Appropriateness Criteria® Post-Treatment Surveillance of Bladder Cancer.

Urothelial cancer is the second most common cancer, and cause of cancer death, related to the genitourinary tract. The goals of surveillance imaging after the treatment of urothelial cancer of the urinary bladder are to detect new or previously undetected urothelial tumors, to identify metastatic disease, and to evaluate for complications of therapy. For surveillance, patients can be stratified into one of three groups: (1) nonmuscle invasive bladder cancer with no symptoms or additional risk factors; (2) nonmuscle invasive bladder cancer with symptoms or additional risk factors; and (3) muscle invasive bladder cancer. This article is a review of the current literature for urothelial cancer and resulting recommendations for surveillance imaging. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

ACR Appropriateness Criteria® Acute Onset of Scrotal Pain-Without Trauma, Without Antecedent Mass.

An acute scrotum is defined as testicular swelling with acute pain and can reflect multiple etiologies including epididymitis or epididymo-orchitis, torsion of the spermatic cord, or torsion of the testicular appendages. Quick and accurate diagnosis of acute scrotum and its etiology with imaging is necessary because a delayed diagnosis of torsion for as little as 6 hours can cause irreparable testicular damage. Ultrasound duplex Doppler of the scrotum is usually appropriate as the initial imaging for the acute onset of scrotal pain without trauma or antecedent mass in an adult or child. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

A nonafluoro nucleoside as a sensitive 19f NMR probe of nucleic acid conformation.

A nucleoside carrying a perfluorinated tert-butyl group ( 4) was prepared by a Sonogashira coupling of 5-iodo-2'-deoxyuridine with 4,4,4-trifluoro-3,3-bis(trifluoromethyl)-1-butyne in nearly quantitative yield and subsequently incorporated into DNA oligomers. Thermal denaturation studies showed that 4 had a negligible effect on duplex stability when compared to thymidine. Transition from single strand to duplex was monitored by (19)F NMR spectroscopy at micromolar concentrations of oligomers, demonstrating the sensitivity of 4 as an NMR reporter nucleoside.

Prediction of miscarriage in women with viable intrauterine pregnancy-A systematic review and diagnostic accuracy meta-analysis.

Both ultrasound and biochemical markers either alone or in combination have been described in the literature for the prediction of miscarriage. We performed this systematic review and meta-analysis to determine the best combination of biochemical, ultrasound and demographic markers to predict miscarriage in women with viable intrauterine pregnancy. The electronic database search included Medline (1946-June 2017), Embase (1980-June 2017), CINAHL (1981-June 2017) and Cochrane library. Key MESH and Boolean terms were used for the search. Data extraction and collection was performed based on the eligibility criteria by two authors independently. Quality assessment of the individual studies was done using QUADAS 2 (Quality Assessment for Diagnostic Accuracy Studies-2: A Revised Tool) and statistical analysis performed using the Cochrane systematic review manager 5.3 and STATA vs.13.0. Due to the diversity of the combinations used for prediction in the included papers it was not possible to perform a meta-analysis on combination markers. Therefore, we proceeded to perform a meta-analysis on ultrasound markers alone to determine the best marker that can help to improve the diagnostic accuracy of predicting miscarriage in women with viable intrauterine pregnancy. The systematic review identified 18 eligible studies for the quantitative meta-analysis with a total of 5584 women. Among the ultrasound scan markers, fetal bradycardia (n=10 studies, n=1762 women) on hierarchical summary receiver operating characteristic showed sensitivity of 68.41%, specificity of 97.84%, positive likelihood ratio of 31.73 (indicating a large effect on increasing the probability of predicting miscarriage) and negative likelihood ratio of 0.32. In studies for women with threatened miscarriage (n=5 studies, n=771 women) fetal bradycardia showed further increase in sensitivity (84.18%) for miscarriage prediction. Although there is gestational age dependent variation in the fetal heart rate, a plot of fetal heart rate cut off level versus log diagnostic odds ratio showed that at ≤110 beat per minutes the diagnostic power to predict miscarriage is higher. Other markers of intra uterine hematoma, crown rump length and yolk sac had significantly decreased predictive value. Therefore in women with threatened miscarriage and presence of fetal bradycardia on ultrasound scan, there is a role for offering repeat ultrasound scan in a week to ten days interval.

ACR Appropriateness Criteria® Pretreatment Staging of Muscle-Invasive Bladder Cancer.

Muscle-invasive bladder cancer (MIBC) has a tendency toward urothelial multifocality and is at risk for local and distant spread, most commonly to the lymph nodes, bone, lung, liver, and peritoneum. Pretreatment staging of MIBC should include imaging of the urothelial upper tract for synchronous lesions; imaging of the chest, abdomen, and pelvis for metastases; and MRI pelvis for local staging. CT abdomen and pelvis without and with contrast (CT urogram) is recommended to assess the urothelium and abdominopelvic organs. Pelvic MRI can improve local bladder staging accuracy. Chest imaging is also recommended with chest radiograph usually being adequate. FDG-PET/CT may be appropriate to identify nodal and metastatic disease. Chest CT may be useful in high-risk patients and those with findings on chest radiograph. Nonurogram CT and MRI of the abdomen and pelvis are usually not appropriate, and neither is radiographic intravenous urography, Tc-99m whole body bone scan, nor bladder ultrasound for pretreatment staging of MIBC. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

PRODOC: a resource for the comparison of tethered protein domain architectures with in-built information on remotely related domain families.

PROtein Domain Organization and Comparison (PRODOC) comprises several programs that enable convenient comparison of proteins as a sequence of domains. The in-built dataset currently consists of approximately 698 000 proteins from 192 organisms with complete genomic data, and all the SWISSPROT proteins obtained from the Pfam database. All the entries in PRODOC are represented as a sequence of functional domains, assigned using hidden Markov models, instead of as a sequence of amino acids. On average 69% of the proteins in the proteomes and 49% of the residues are covered by functional domain assignments. Software tools allow the user to query the dataset with a sequence of domains and identify proteins with the same or a jumbled or circularly permuted arrangement of domains. As it is proposed that proteins with jumbled or the same domain sequences have similar functions, this search tool is useful in assigning the overall function of a multi-domain protein. Unique features of PRODOC include the generation of alignments between multi-domain proteins on the basis of the sequence of domains and in-built information on distantly related domain families forming superfamilies. It is also possible using PRODOC to identify domain sharing and gene fusion events across organisms. An exhaustive genome-genome comparison tool in PRODOC also enables the detection of successive domain sharing and domain fusion events across two organisms. The tool permits the identification of gene clusters involved in similar biological processes in two closely related organisms. The URL for PRODOC is http://hodgkin.mbu.iisc.ernet.in/~prodoc.

A Study of Vitiligo in Type 2 Diabetic Patients.

CONTEXT: Diabetes mellitus is associated with many skin manifestations including vitiligo. Vitiligo occurs more commonly in Type 1 diabetes mellitus. A few recent studies have shown its increased occurrence in Type 2 diabetes mellitus. AIMS: This study aims to study the prevalence of vitiligo in Type 2 diabetic patients and to compare the prevalence of vitiligo in age- and sex-matched group of nondiabetic population. SETTINGS AND DESIGN: The present study was a hospital-based cross-sectional study conducted in the Department of Dermatology in a tertiary care hospital. SUBJECTS AND METHODS: Six hundred consecutive consenting patients of Type 2 diabetes were included in the study group and age- and sex-matched controls were healthy nondiabetic adult volunteers attending the Department of Dermatology. Fasting and postprandial blood sugar levels were done. A complete history, physical examination, and wood's lamp examination to detect vitiligo were conducted. In all those with vitiligo, the type of vitiligo was noted. STATISTICAL ANALYSIS USED: Data were analyzed using SPSS software version 20.0. Comparison between the presence of vitiligo in cases and controls was done using Chi-square test with P = 0.05 for significance. RESULTS: Vitiligo was seen in 12% of cases and 6% of control group which was statistically significant (P < 0.01). There was no significant difference between cases and controls with respect to type of vitiligo. CONCLUSIONS: Vitiligo can occur in Type 2 diabetics as seen in our study and few other recent studies. The exact pathogenesis is not very clear and needs further consideration.

Synthesis, anti-angiogenic and DNA cleavage studies of novel N-(4-methyl-3-((4-(pyridin-3-yl)pyrimidin-2-yl)amino)phenyl)piperidine-4-carboxamide derivatives.

A series of novel N-(4-methyl-3-((4-(pyridin-3-yl)pyrimidin-2-yl)amino)phenyl)piperidine-4-carboxamide derivatives 10(a-f), 12(a-c) and 14(a-c) were synthesized and characterized by FTIR, 1H-NMR, mass spectral and elemental analysis. The efficacy of these derivatives to inhibit in vivo angiogenesis was evaluated using chick chorioallantoic membrane (CAM) model and their DNA cleavage abilities were evaluated after incubating with calf thymus DNA followed by gel electrophoresis. These novel piperidine analogues efficiently blocked the formation of blood vessels in vivo in CAM model and exhibited differential migration and band intensities in DNA binding/cleavage assays. Among the tested compounds 10a, 10b, 10c, 12b, 14b and 14c showed significant anti-angiogenic and DNA cleavage activities compared to their respective controls and the other derivatives used in this study. These observations suggest that the presence of electron donating and withdrawing groups at positions 2, 3 and 4 of the phenyl ring of the side chain may determine their potency and as anticancer agents by exerting both anti-angiogenic and cytotoxic effects .

Role of serum biomarkers in the prediction of outcome in women with threatened miscarriage: a systematic review and diagnostic accuracy meta-analysis.

BACKGROUND: Threatened miscarriage affects one in five women and is associated with significant emotional distress. The uncertainty around the prognosis of threatened miscarriage makes it equally challenging to the healthcare professionals. Various biochemical markers have been investigated in the past to predict the outcome of threatened miscarriage; however, the results have been conflicting. Therefore, we have conducted a systematic review and meta-analysis to determine the diagnostic accuracy of biochemical markers in predicting the outcome in women presenting with threatened miscarriage. METHODS: This is a systematic review and meta-analysis of prospective studies that investigated biochemical markers to determine outcomes for women with threatened miscarriage at 5-23 weeks gestational age. Electronic databases were searched up to June 2015 and study quality assessment was performed using QUADAS-2 (Quality Assessment for Diagnostic Accuracy Studies-2: A Revised Tool) for evaluating the diagnostic accuracy studies. Statistical analysis was performed using the Cochrane systematic review software. RESULTS: A total of 19 studies were included in the qualitative data synthesis of which 15 (including 1263 women) were eligible for the meta-analysis. The review highlights the role of biochemical markers serum progesterone, hCG, pregnancy associated plasma protein A, estradiol and cancer antigen 125 (CA 125) in the prediction of outcome in women with threatened miscarriage. Interestingly, serum CA 125 appears to be the most promising marker (n = 648 women in seven studies), whereas serum progesterone and hCG are less useful once fetal viability is established. The summary receiver operating characteristics for CA 125 showed a sensitivity of 90% (95% confidence interval (CI) 83-94%), specificity of 88% (95% CI 79-93%), positive likelihood ratio of 7.86 (95% CI 4.23-14.60) and negative likelihood ratio of 0.10 (95% CI 0.06-0.20). The inverse of negative likelihood ratio was 9.31 (95% CI 5-17.1) indicating that a negative test is likely to identify those who are likely to continue with the pregnancy. Serum estradiol was the next best marker with a sensitivity of 45% (95% CI 6-90%), a specificity of 87% (95% CI 81-92%), a positive likelihood ratio of 3.72 (95% CI 1.01-13.71) and a negative likelihood ratio of 0.62 (95% CI 0.20-1.84). CONCLUSIONS: In women with threatened miscarriage, serum CA 125 has high predictive value in identifying pregnancies that are 'likely to continue', whereas the most commonly used biomarkers of serum hCG and progesterone are not useful in predicting outcome of a pregnancy with a viable fetus. Other markers such as inhibin A and a combination of markers need to be investigated to hopefully improve the prediction of outcome in women with threatened miscarriage.

Interaction interfaces of protein domains are not topologically equivalent across families within superfamilies: Implications for metabolic and signaling pathways.

Using a data set of aligned protein domain superfamilies of known three-dimensional structure, we compared the location of interdomain interfaces on the tertiary folds between members of distantly related protein domain superfamilies. The data set analyzed is comprised of interdomain interfaces, with domains occurring within a polypeptide chain and those between two polypeptide chains. We observe that, in general, the interfaces between protein domains are formed entirely in different locations on the tertiary folds in such pairs. This variation in the location of interface happens in protein domains involved in a wide range of functions, such as enzymes, adapters, and domains that bind protein ligands, or cofactors. While basic biochemical functionality is preserved at the domain superfamily level, the effect of biochemical function on protein assemblies is different in these protein domains related by superfamily. The divergence between proteins, in most cases, is coupled with domain recruitment, with different modes of interaction with the recruited domain. This is in complete contrast to the observation that in closely related homologous protein domains, almost always the interaction interfaces are topologically equivalent. In a small subset of interacting domains within proteins related by remote homology, we observe that the relative positioning of domains with respect to one another is preserved. Based on the analysis of multidomain proteins of known or unknown structure, we suggest that variation in protein-protein interactions in members within a superfamily could serve as diverging points in otherwise parallel metabolic or signaling pathways. We discuss a few representative cases of diverging pathways involving domains in a superfamily.

Identification of a heterodimer-specific epitope present in human chorionic gonadotrophin (hCG) using a monoclonal antibody that can distinguish between hCG and human LH.

Human chorionic gonadotrophin (hCG) is secreted during early pregnancy and is required for implantation and maintenance of the pregnancy. Active or passive immunoneutralization of hCG results in termination of pregnancy and this forms the basis of the hCG-based female contraceptive vaccine. However, the beta subunit of hCG possesses 85% sequence homology with the first 114 amino acids of the beta subunit of pituitary human LH (hLH), which is required for ovulation and maintenance of the corpus luteum function during the menstrual cycle. Immunization against hCG or its beta subunit leads to generation of antibodies that can neutralize hLH due to many shared epitopes and hence may cause abnormal menstrual cycles. Therefore, it is essential to identify epitopes that are different in the two hormones. In the present study, we report a monoclonal antibody (MAb) specific for hCG that shows no binding to the isolated subunits. Interestingly, the MAb also does not bind hLH at all. The epitope mapping analysis revealed that this antibody recognizes a unique discontinuous epitope present only in the heterodimeric hCG and is distinct from the unique C-terminal extension of hCG beta that is absent in hLH beta. The MAb, either as IgG or its recombinant single-chain variable region fragment, inhibited the response to hCG, but not to hLH. Thus, the epitope recognized by this MAb is an ideal candidate antigen for immunocontraception.

Interaction preferences across protein-protein interfaces of obligatory and non-obligatory components are different.

BACKGROUND: A polypeptide chain of a protein-protein complex is said to be obligatory if it is bound to another chain throughout its functional lifetime. Such a chain might not adopt the native fold in the unbound form. A non-obligatory polypeptide chain associates with another chain and dissociates upon molecular stimulus. Although conformational changes at the interaction interface are expected, the overall 3-D structure of the non-obligatory chain is unaltered. The present study focuses on protein-protein complexes to understand further the differences between obligatory and non-obligatory interfaces. RESULTS: A non-obligatory chain in a complex of known 3-D structure is recognized by its stable existence with same fold in the bound and unbound forms. On the contrary, an obligatory chain is detected by its existence only in the bound form with no evidence for the native-like fold of the chain in the unbound form. Various interfacial properties of a large number of complexes of known 3-D structures thus classified are comparatively analyzed with an aim to identify structural descriptors that distinguish these two types of interfaces. We report that the interaction patterns across the interfaces of obligatory and non-obligatory components are different and contacts made by obligatory chains are predominantly non-polar. The obligatory chains have a higher number of contacts per interface (20 +/- 14 contacts per interface) than non-obligatory chains (13 +/- 6 contacts per interface). The involvement of main chain atoms is higher in the case of obligatory chains (16.9 %) compared to non-obligatory chains (11.2 %). The beta-sheet formation across the subunits is observed only among obligatory protein chains in the dataset. Apart from these, other features like residue preferences and interface area produce marginal differences and they may be considered collectively while distinguishing the two types of interfaces. CONCLUSION: These results can be useful in distinguishing the two types of interfaces observed in structures determined in large-scale in the structural genomics initiatives, especially for those multi-component protein assemblies for which the biochemical characterization is incomplete.