U01.01.033 Elastin

Elastin is an essential extracellular matrix protein responsible for providing elasticity to tissues. It plays a critical role in the structure and function of various organs and systems, including the skin, lungs, arteries, and ligaments. Below is a breakdown of important points related to elastin for USMLE Step 1 preparation.

Key Characteristics of Elastin

Property	Details
Location	Skin, lungs, large arteries, elastic ligaments, vocal cords, ligamenta flava (vertebrae)
Composition	Rich in nonhydroxylated proline, glycine, and lysine (compared to collagen’s hydroxylated residues)
Structure	Tropoelastin with fibrillin scaffolding, cross-linked extracellularly
Elastic Properties	Stretchy protein that can alternate between stretched and relaxed conformations

Mechanism and Function

Cross-linking: Elastin acquires its elastic properties through extracellular cross-linking.
Elastase Breakdown: Elastin is broken down by elastase, an enzyme that is normally inhibited by α1-antitrypsin.
α1-Antitrypsin Deficiency: In the absence of α1-antitrypsin, elastase activity is unopposed, leading to conditions like chronic obstructive pulmonary disease (COPD).

Clinical Relevance

Condition	Cause and Pathophysiology	Key Findings
Marfan Syndrome	Autosomal dominant disorder due to FBN1 gene mutation on chromosome 15, leading to defective fibrillin, which affects elastin	Tall stature, long extremities, hypermobile joints, arachnodactyly, pectus carinatum/excavatum, aortic aneurysm/dissection, mitral valve prolapse, subluxation of lenses
Aging Effects on Elastin	Aging decreases dermal collagen and elastin synthesis but cross-linking remains normal	Reduced elasticity and strength in tissues with aging

Points to Remember

Elastin’s Role: Provides elasticity in tissues such as the skin, lungs, arteries, and ligaments.
Aging Effects: Decreased elastin and collagen synthesis with age.
Cross-Linking: Extracellular cross-linking of elastin is essential for its elastic properties.
Elastase Activity: Unopposed elastase due to α1-antitrypsin deficiency can lead to conditions like COPD.
Marfan Syndrome: Caused by a mutation in the FBN1 gene, leading to defective fibrillin and a range of clinical features, including aortic aneurysm.

Learning Objective

Understand the structural and functional properties of elastin, its clinical implications in disorders like Marfan syndrome and α1-antitrypsin deficiency, and its role in tissue elasticity.

USMLE Step 1 Review Series

Curriculum