ALLELIC HETEROGENEITY IN COL7A1: A CONDITION IN DEB DEB – DYSTROPHIC EPIDERMOLYSIS BULLOSA
AUTHOR: POOJA P
ABSTRACT Epidermolysis bullosa refers to a group of genodermatoses that is caused by mutations in anchoring fibrils, which in-turn affects the integrity of epithelial layers of skin and causes blisters. Blisters happen in response to mechanical trauma in these patients. Dystrophic Epidermolysis Bullosa (DEB) is a subtype of Epidermolysis bullosa (EB) and has very severe phenotypes. DEB is due to mutation in collagen 7 that is a major component of anchoring fibril. Some patients show severe phenotypes such as recurrent blistering, webbed/ fused fingers and toes. In this study we conducted genotype phenotype correlation to see if different mutations could cause difference in the level of severity in DEB patient phenotype. We also predicted the possibilities in such an instance. For which we conducted genotype phenotype correlation and the structural effects of protein were examined with the help of homology modelling. It is found that phenotypic severity differs in patients and the level of severity is not due to the type of mutation. Instead, an increase or decrease in the stability of collagen 7 protein upon mutation affect level of phenotypic severity seen in these patients.
CO-AUTHOR: RAVI HIRAMAGALORE
MATERIALS AND METHODS PART 1 • Total 10 DEB patients were recruited for the study • Patients were recruited from Manipal hospital, Indira Gandhi institute of child health, referrals • Clinical phenotype details were collected from these patients • Clinical exome was done to all these patients to find out the mutation
PART 2
Severe phenotypes such as webbing and scars in extrimities are not seen in glutamic acid substitution patients. On the other hand, not everyone with Glycine substitution showed severe phenotype. Thus, it is clear that not only the type of mutation is responsible for severity of phenotype seen in patients.
RESULTS PART 2
DDG VALUE PATIENT Glycine (PROTEIN NO. substitution STABILITY)
QUESTIONS ADDRESSED PART 1 • WHETHER DIFFERENT MUTATIONS IN COL7A1 CAUSES DIFFERENCE IN THE LEVEL OF SEVERITY IN DEB PATIENT PHENOTYPE ? PART 2 • IF SO WHY? (What are the possible reasons)
OBJECTIVES PART 1 Genotype phenotype correlation
PROTEIN STABILITY MEASURE (DDG - DELTA DELTA G) DDG < -0.5 means (large decrease of stability), DDG > 0.5 means (increase Of stability), and -0.5 <= DDG <= 0.5 means (neutral stability)
RESULTS PART 1 Three types of mutations were observed in patient cohort and the below graphs depicts percentage of patients show the phenotypes mentioned in x-axis n=6
Glu748Lys - P08 (homology modelling)
DDG VALUE Premature PATIENT Glutamic acid (PROTEIN PATIENT terminal NO. substitution STABILITY) NO. codon
P01
Gly2749Arg
- 0.7
P07
Glu282Asp
- 0.15
P09
Gln1675Ter
P02
Gly2034Arg
- 0.46
P08
Glu748Lys
- 0.21
P10
Arg1630Ter
P03
Val1895Serf s Ter20
P03
Gly2236Arg
0
P04
Gly2659Glu
1.01
P05
Gly2351Arg
- 0.87
P06
Gly2749Glu
0.74
• PATIENTS WITH DDG VALUE (< -0.50 AND > 0.5) AND PATIENTS WITH PRE TERMINATION CODON(blue) HAS MORE SEVERE PHENOTYPE SUCH AS WEBBING, FUSION AND SCARS IN EXTREMITIES • OTHER PATIENTS(black) DOES NOT SHOW WEBBING AND SCARS OR BLISTERS IN EXTREMITIES
CONCLUSION • More glycine substitutions are seen in our study
PART 2 Structural effects of mutations found in col7a1 and linking it with phenotype severity.
• Modelling of proteins (homology modelling) can help in better understanding of structure function relationship.
• It is evident that mutations affect the stability of proteins.
• Model the structure of COL7A1. • Study the structural effects of mutation (Protein stability upon mutation)
• It is also shown that this change in stability of proteins have an effect on disease phenotype. SOURCE : Quan, Lijun et al. “STRUM: structure-based prediction of protein stability changes upon single-point mutation.” Bioinformatics (Oxford, England) vol. 32,19 (2016): 2936-46.
SOURCE : UCSF Chimera