TPM3 (Tropomyosin 3) Notes - ISOFORMS Project

Key Isoform Biology

TPM3 has 7 named isoforms with tissue-specific expression, similar to TPM1.

Tissue-Specific Isoforms

Isoform UniProt ID Synonym Tissue Key Feature
Isoform 1 P06753-1 Skeletal muscle Slow skeletal muscle Type I fibers
Isoform 2 P06753-2 TM30nm, Cytoskeletal Non-muscle cells 30nm variant

Functional Distinctions

Skeletal muscle isoform (1):
- Expressed in slow-twitch (type I) muscle fibers
- Part of thin filament regulatory complex
- Essential for proper muscle contraction

Cytoskeletal isoforms (2, 3, etc.):
- TM30nm - shorter variant (248 AA vs 285 AA for muscle)
- Functions in non-muscle actin cytoskeleton
- Different actin binding characteristics

Disease Associations

CMYO4A: Congenital myopathy 4A
- Autosomal dominant
- Muscle weakness in infancy/childhood
- Features: hypotonia, respiratory insufficiency
- Muscle biopsy shows nemaline rods, "cap" structures, fiber-type disproportion

UniProt states:

"A muscular disorder characterized by onset of muscle weakness in infancy or childhood. Most affected individuals show mildly delayed motor development, hypotonia, generalized muscle weakness"

Relationship to TPM1

TPM1 and TPM3 are both members of the tropomyosin family but:
- TPM1: More associated with cardiac/smooth muscle function
- TPM3: More associated with slow skeletal muscle and cytoskeleton

Expected Annotation Issues

  1. "Muscle contraction" - applies to muscle isoforms
  2. "Actin binding" - all isoforms but with different properties
  3. "Cytoskeleton organization" - primarily cytoskeletal isoforms

GOA Annotation Count: 39