Protein Function
Actin and Myosin
Introduction
• Organisms move. Cells move. Organelles and macromolecules within
cells move.
• Most of these movements arise from the activity of a class of protein-
based molecular motors. Fueled by chemical energy, usually derived
from ATP.
• Motor proteins mediate the contraction of muscles, the migration of
organelles along microtubules, the rotation of bacterial flagella, and the
movement of some proteins along DNA.
Actin and Myosin
• The major proteins of muscle are actin and myosin.
• The contractile force of muscle is generated by the interaction of
myosin and actin.
• These proteins are arranged in filaments that undergo transient
interactions and slide past each other to bring about contraction.
• Together, actin and myosin make up more than80% of the protein
mass of muscle
, Myosin
• Myosin (520-KD) has
1. six subunits: two heavy chains (each of 220-KD) and
2. four light chains (each of20-KD).
The heavy chains account for much of the overall structure.
• At their carboxyl termini, they are arranged as extended α helices,
wrapped around each other in a fibrous (coiled coil, tail).
• At its amino terminus, each heavy chain has a large globular domain
containing a site where ATP is hydrolyzed.
• The light chains are associated with the globular domains.
Both Actin & Myosin have globular portions (G-actin and the head of
myosin).
Actin and Myosin
Introduction
• Organisms move. Cells move. Organelles and macromolecules within
cells move.
• Most of these movements arise from the activity of a class of protein-
based molecular motors. Fueled by chemical energy, usually derived
from ATP.
• Motor proteins mediate the contraction of muscles, the migration of
organelles along microtubules, the rotation of bacterial flagella, and the
movement of some proteins along DNA.
Actin and Myosin
• The major proteins of muscle are actin and myosin.
• The contractile force of muscle is generated by the interaction of
myosin and actin.
• These proteins are arranged in filaments that undergo transient
interactions and slide past each other to bring about contraction.
• Together, actin and myosin make up more than80% of the protein
mass of muscle
, Myosin
• Myosin (520-KD) has
1. six subunits: two heavy chains (each of 220-KD) and
2. four light chains (each of20-KD).
The heavy chains account for much of the overall structure.
• At their carboxyl termini, they are arranged as extended α helices,
wrapped around each other in a fibrous (coiled coil, tail).
• At its amino terminus, each heavy chain has a large globular domain
containing a site where ATP is hydrolyzed.
• The light chains are associated with the globular domains.
Both Actin & Myosin have globular portions (G-actin and the head of
myosin).
