Types of Motor protein, there introduction, structure, location and function. Mainly, Actin, Myosin, keratin and dynein.

1. MOTOR PROTEINS
Kautilya M. Nyalkalkar : BBT-2-18018
Arjit Ghosh : BBT-2-18007
Arjeet Dedhe : BBT-2-18006
Shaunak Iyer : BBT-2-17043

2. INDEX
• Motor proteins
• Types
– Myosin
– Actin
– Keratin
– Dynein
• Reference

3. Motor Proteins
Motor proteins belong to a class of molecular motors that can move along the cytoplasm of animal
cells. They convert chemical energy into mechanical work by the hydrolysis of ATP. Flagellar rotation,
however, is powered by a proton pump.
Where Actin and Myosin are microfilament actin motors, Keratin is structural motor protein and
dynein is microtubule motor protein.

4. Mysoin
• Introduction:
– Myosin's are motor proteins that interact with actin filaments and couple hydrolysis of ATP to conformational changes that result
in the movement of myosin and an actin filament relative to each other.
– Thirteen members of the myosin gene family have been identified by genomic analysis. Myosin I and myosin II, the most
abundant and thoroughly studied of the myosin proteins, are present in nearly all eukaryotic cells. A less-common isoform,
myosin V, also has been isolated and characterized. Although the specific activities of these myosins differ, they all function as
motor proteins. Myosin II powers muscle contraction and cytokinesis, whereas myosins I and V are involved in cytoskeleton-
membrane interactions such as the transport of membrane vesicles.
– All myosins are regulated in some way by Ca2+; however, because of the differences in their light chains, the different myosins
exhibit different responses to Ca2+ signals in the cell.
– They work in contrast with Actin proteins.

5. • Structure:
– All myosins are composed of one or two heavy chains and several light
chains. And there body is composed of Head, Neck and Tail:
• Head: - The globular head domain contains actin- and ATP-binding
sites and is responsible for generating force.
• Neck: - Adjacent to the head domain lies the α-helical, which is
associated with light chains.
• Tail: - contains the binding sites that determine the specific
activities of a particular myosin
– Myosin II, a dimeric molecule with a long rodlike tail domain, assembles
into bipolar thick filaments that take part in muscle contraction.
– Myosin II contains two different light chains (called essential and
regulatory light chains); both are Ca2+-binding proteins but differ from
calmodulin in their Ca2+-binding properties.

6. • Location:
– Skeletal muscle myosin, the most conspicuous of the
myosin superfamily due to its abundance in muscle
fibers, was the first to be discovered.
– This protein makes up part of the sarcomere and forms
macromolecular filaments composed of multiple
myosin subunits.
– Similar filament-forming myosin proteins were found
in cardiac muscle, smooth muscle, and nonmuscle
cells.

7. • Functions:
– In all myosins, the head domain is a specialized ATPase that is able to couple the hydrolysis of ATP with motion. A critical
feature of the myosin ATPase activity is that it is actin-activated. In the absence of actin, solutions of myosin slowly convert ATP
into ADP and phosphate.
– Sliding Filament theory: -
• the movement of fluorescent-labeled actin filaments along a bed of myosin molecules is observed in a fluorescence
microscope. Because the myosin molecules are tethered to a coverslip, they cannot move; thus any force generated by
interaction of myosin heads with actin filaments forces the filaments to move along the myosin. If ATP is present, added
actin filaments can be seen to glide along the surface of the coverslip; if ATP is absent, no filament movement is
observed.
• The power stroke occurs at the release of phosphate from the myosin molecule after the ATP hydrolysis while myosin is
tightly bound to actin. The effect of this release is a conformational change in the molecule that pulls against the actin.
The release of the ADP molecule leads to the so-called rigor state of myosin. The binding of a new ATP molecule will
release myosin from actin. ATP hydrolysis within the myosin will cause it to bind to actin again to repeat the cycle. The
combined effect of the myriad power strokes causes the muscle to contract.

8. Actin
• Introduction:
– Actin is a family of globular multi-functional proteins that form microfilaments. It is found in essentially all eukaryotic cells ,
where it may be present at a concentration of over 100 μM; its mass is roughly 42-kDa, with a diameter of 4 to 7 nm.
– An actin protein is the monomeric subunit of two types of filaments in cells: microfilaments, one of the three major components
of the cytoskeleton, and thin filaments, part of the contractile apparatus in muscle cells. It can be present as either a
free monomer called G-actin (globular) or as part of a linear polymer microfilament called F-actin (filamentous), both of which
are essential for such important cellular functions as the mobility and contraction of cells during cell division.

9. • Structure:
– Actin is one of the most abundant proteins in eukaryotes, where it is found throughout the cytoplasm. In fact, in muscle fibres it
comprises 20% of total cellular protein by weight and between 1% and 5% in other cells.
– Cellular actin has two forms: monomeric globules called G-actin and polymeric filaments called F-actin.

10. • Location:
– The actin protein is found in both the cytoplasm and the cell nucleus.
– Its location is regulated by cell membrane signal transduction pathways that integrate the stimuli that a cell receives stimulating
the restructuring of the actin networks in response.
– Actin filaments are particularly stable and abundant in muscle fibres. Within the sarcomere (the basic morphological and
physiological unit of muscle fibres) actin is present in both the I and A bands; myosin is also present in the latter.

11. • Functions:
– Various types of actin networks (made of actin filaments) give mechanical support to cells, and provide trafficking routes
through the cytoplasm to aid signal transduction.
– Rapid assembly and disassembly of actin network enables cells to migrate .
– In metazoan muscle cells, to be the scaffold on which myosin proteins generate force to support muscle contraction.

12. Keratin
• Introduction:
– Keratin represents a group of insoluble, usually high-sulfur content and filament-forming proteins, constituting the bulk of
epidermal appendages such as hair, nails etc claws. Keratin is considered ‘dead tissues’ and are the toughest biological materials.
– The human genome encodes 54 functional keratin genes which are located in two clusters on chromosomes 12 and 17. This
suggests that they have originated from a series of gene duplications on these chromosomes.

13. • Structure:
– Keratins can be classified as α- and β-types. Both show a characteristic filament-matrix structure. Both are embedded in an
amorphous keratin matrix. The mechanical response of α-keratin has been studied and shows a high reversible elastic
deformation. Thus, they can be also be considered ‘biopolymers’.
– Fibrous keratin molecules supercoil and thus are very stable. They form filaments, consisting of multiple copies of the
keratin monomer. The major force that keeps the coiled structure is hydrophobic interactions.
– In addition to intra- and intermolecular hydrogen bonds, the distinguishing feature of keratins is the presence of large amounts of
the sulfur-containing amino acid cysteine, required for disulfide bridges that confer additional strength and rigidity by
permanent, thermally stable crosslinking.

14. • Location:
– Keratin can be found in: -
• human tooth enamel,
• fingernails,
• toenails,
• hair,
• and in the outer layer of the human skin.

15. • Functions:
– To hold skin cells together to form a barrier.
– To form the outermost layer of our skin, that protects us from the environment.
– Keratin filaments provide a scaffold for epithelial cells and tissues to sustain mechanical stress.
– They need to maintain their structural integrity to ensure mechanical resilience.
– Keratin also helps in cell signaling, cell transport, cell compartmentalization and cell differentiation.

16. Dynein
• Introduction:
– Dynein is a family of cytoskeletal motor proteins that move along microtubules in cells. They convert the chemical energy stored
in ATP to mechanical work. Dynein transports various cellular cargos, provides forces and displacements important in mitosis,
and drives the beat of eukaryotic cilia and flagella. All of these functions rely on dynein's ability to move towards the minus-end
of the microtubules, known as retrograde transport, thus, they are called "minus-end directed motors".
– Dyneins can be divided into two groups: cytoplasmic dyneins and axonemal dyneins, which are also called ciliary or flagellar
dyneins.
• Axonemal
– heavy chain: DNAH1, DNAH2, DNAH3, DNAH5, DNAH6, DNAH7, DNAH8, DNAH9, DNAH10, DNAH11,
DNAH12, DNAH13, DNAH14, DNAH17
– intermediate chain: DNAI1, DNAI2
– light intermediate chain: DNALI1
– light chain: DNAL1, DNAL4
• Cytoplasmic
– heavy chain: DYNC1H1, DYNC2H1
– intermediate chain: DYNC1I1, DYNC1I2
– light intermediate chain: DYNC1LI1, DYNC1LI2, DYNC2LI1
– light chain: DYNLL1, DYNLL2, DYNLRB1, DYNLRB2, DYNLT1, DYNLT3

17. • Structure:
– Cytoplasmic Dynein
• Cytoplasmic dynein, which has a molecular mass of about 1.5 megadaltons (MDa), is a dimer of dimers, containing
approximately twelve polypeptide subunits: two identical "heavy chains", 520 kDa in mass, which contain the ATPase
activity and are thus responsible for generating movement along the microtubule; two 74 kDa intermediate chains which
are believed to anchor the dynein to its cargo; two 53–59 kDa light intermediate chains; and several light chains.
– Axonemal Dynein
• Axonemal dyneins come in multiple forms that contain either one, two or three non-identical heavy chains (depending
upon the organism and location in the cilium). Each heavy chain has a globular motor domain with a doughnut-shaped
structure believed to resemble that of other AAA proteins, a coiled coil "stalk" that binds to the microtubule, and an
extended tail (or "stem") that attaches to a neighboring microtubule of the same axoneme. Each dynein molecule thus
forms a cross-bridge between two adjacent microtubules of the ciliary axoneme.

18. • Functions:
– Mitotic spindle positioning:
• Cytoplasmic dynein positions the spindle at the site of cytokinesis by anchoring to the cell cortex and pulling on astral
microtubules emanating from centrosome. Budding yeast have been a powerful model organism to study this process and
has shown that dynein is targeted to plus ends of astral microtubules and delivered to the cell cortex via an offloading
mechanism.
– Viral replication:
• Dynein and kinesin can both be exploited by viruses to mediate the viral replication process. Many viruses use the
microtubule transport system to transport nucleic acid/protein cores to intracellular replication sites after invasion past the
cell membrane. Suggesting that proline-rich sequences may be a major binding site for viruses that co-opts Dynein.
– Axonemal dynein causes sliding of microtubules in the axonemes of cilia and flagella and is found only in cells that have those
structures.

19. REFERENCE
• https://www.news-medical.net/life-sciences/Actin-Motor-Proteins.aspx
• https://www.ncbi.nlm.nih.gov/books/NBK21724/
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3972880/
• https://en.wikipedia.org/wiki/Motor_protein
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2736122/