MYOSIN STRUCTURE, FUNCTION AND MODE OF ACTION IN HUMANS

A brief about the mode of action of myosin , it's structure and function in human muscle cells and many other processes

1. MYOSIN STRUCTURE FUNCTION AND MODE OF ACTION RISHI SINGH ROLL NO: 152 MSC 1- BIOTECH 1

2. INTRODUCTION ORGANISMS MOVES.CELLS MOVE. ORGANELLES AND MACROMOLECULES WITHIN THE CELLS MOVE. MOST OF THESE MOVEMENTS ARISE FROM ACTIVITY OF A FASCINATING CLASS OF PROTEIN BASED MOLECULAR MOTORS ;FUELED BY CHEMICAL ENERGY,USUALLY DERIVED FROM ATP. ONE SUCH PROTEIN BASED MOLECULAR MOTOR IS MYOSIN MYOSIN IS A MOTOR PROTEIN THAT CONVERTS CHEMICAL ENERGY OF ATP HYDROLYSIS TO MECHANICAL ENERGY OF MOVEMENT 2

3. HISTORICAL BACKGROUND MOLECULAR CHARACTERIZATION OF MUSCLE DIDN’T OCCUR OVERNIGHT: 1859 WILLI KUHNE MYOSIN FROM MUSCLE TISSUE 1941 ALBERT SZENT MYOSIN-A AND MYOSIN-B IN 1948 HUGH HUXLEY “SLIDING FILAMENT MODEL” LATER,HUXLEY AND HANSON OBSERVED RABBIT MUSCLE FIBRES UNDER DIFFERENT EXPERIMENTAL CONDITIONS AND CONCLUDED THE FOLLOWING :- A-BAND CONSISTS OF MYOSIN ACTIN WAS PRESENT THROUGHOUT THE SARCOMERE WHEN ATP WAS ADDED MUSCLE SLOWLY CONTRACTS AND I-BAND SHORTENS, WHEN MUSCLE RELAXED I-BAND INCREASED IN WIDTH MYOSIN FORMS CROSS BRIDGES WITH ACTIN FIBRES

4. STUCTURE OF MUSCLE MUSCLE BUNDLE OF MUSCLE FIBRES INDIVIDUAL MUSCLE FIBRE MYOFIBRIL SARCOMERE

5. MYOFIBRIL THE BANDS ARE FORMED BY ALTERNATING REGIONS OF GREATER AND LESSER ELECTRON DENSITY CALLED “A-BANDS” AND “I-BANDS” MYOFIBRILS REPEATING UNIT “SARCOMERE ” IS BOUNDED BY Z-DISKS AT CENTRE OF EACH I-BAND

6. MYOFIBRIL THE A-BAND CONTAINS THICK FILAMENTS THE I-BAND CONTAINS THIN FILAMENTS THESE THICK AND THIN FILAMENTS ARE LINKED TOGETHER BY CROSS BRIDGES WHERE THEY OVERLAP MUSCLE CONTRACTION RESULTS FROM DECREASE IN LENGTH OF SARCOMERE CAUSED BY REDUCTION IN LENGTH OF I-BANDS

7. STRUCTURE OF MYOSIN MYOSIN HAS 6 POLYPEPTIDE CHAINS/SUBUNITS 2 HEAVY CHAINS AND 2 PAIR OF DIFFERENT LIGHT CHAINS(ELC AND RLC) HEAVY CHAIN ACCOUNT FOR MUCH OF OVERALL STRUCTURE N-TERMINAL GLOBULAR DOMAIN(HEAD) C-TERMINAL LONG FIBROUS ALPHA HELICAL TAIL( THE 2 TAILS ASSOCIATE TO FORM A LEFT HANDED COILED COIL) THUS MYOSIN CONSISTS OF LONG ROD LIKE SEGMENTS WITH 2 GLOBULAR HEADS

8. THICK FILAMENTS UNDER PHYSIOLOGICAL CONDITIONS SEVERAL MYOSIN MOLECULES AGGREGATE TO FORM A THICK FILAMENT THE ROD LIKE TAILS PACK END TO END IN A STAGGERED MANNER ;LEAVING THE GLOBULAR HEADS PROJECTING TO THE SIDES ON BOTH ENDS

9. FUCTIONS OF MYOSIN MYOSIN IS PRIMARILY KNOWN FOR ITS ROLE IN MUSCLE CONTRACTION BUT IT ALSO TAKES PART IN VARIOUS CELLULAR PROCESSES WHICH INCLUDE :- CELLULAR TRANSPORT CELL DIVISION CELLULAR MOTILITY MAINTENANCE OF CELL SHAPE

10. CELLULAR TRANSPORT MYOSIN 1 , 2 AND 5 TRANSPORTS VARIOUS CARGO WITHIN THE CELLS MYOSIN MOVE ALONG MICRO-FILAMENTS OR MICROTUBULES CARRYING ORGANELLES ,VESICLES AND OTHER CELLULAR COMPONENTS

11. CELL DIVISION DURING CELL DIVISION MYOSIN 2 IS CRUCIAL FOR CYTOKINESIS MYOSIN FORMS A CONTRACTILE RING JUST BENEATH THE CELL MEMBRANE AT EQUATOR OF DIVIDING CELLS AS MYOSIN 2 CONTRACTS IT PINCHES THE CELL MEMBRANE LEADING TO SEPARATION OF CELL INTO TWO DAUGHTER CELLS

12. CELLULAR MOTILITY MYOSIN IS ESSENTIAL FOR CELL MOTILITY IT ALLOWS CELLS TO MOVE, CHANGE SHAPE AND MIGRATE EX- AMOEBOID MOVEMENT OF WBCs

13. MAINTENANCE OF CELL SHAPE MYOSIN INTERACTS WITH CYTOSKELETON (SPECIFICALLY ACTIN FILAMENTS) TO HELP MAINTAIN CELL SHAPE AND INTEGRITY IT PROVIDES TENSION AND STRUCTURAL SUPPORT TO CELLS

14. MODE OF ACTION OF MYOSIN( MUSCLE CONTRACTION ) IN MUSCLE CONTRACTION THE ACTUAL CONTRACTILE FORCE IS PROVIDED BY ATP

15. MODE OF ACTION OF MYOSIN( MUSCLE CONTRACTION ) MECHANISM OF FORCE GENERATION IN MUSCLES:- ATP BINDS TO MYOSIN HEAD MYOSIN’S ACTIN BINDING SITE OPEN UP AND RELEASE ITS BOUND ACTIN MYOSIN’S ACTIVE SITE CLOSES AROUND THE ATP HYDROLYSIS OF ATP ADP+Pi ; “COCKS” THE MYOSIN HEAD BECAUSE OF WHICH MYOSIN HEAD BECOMES PERPENDICULAR TO THE THICK FILAMENT MYOSIN HEAD BINDS WEAKLY TO THE ACTIN MONOMER THAT IS CLOSER TO THE Z-DISK MYOSIN RELEASES Pi ACTIN BINDING SITE CLOSES RESULTING TRANSIENT STATE IS FOLLOWED BY POWER STROKE ADP IS RELEASED THEREBY COMPLETING THE CYCLE

16. MECHANISM OF FORCE GENERATION IN MUSCLE

17. SLIDING FILAMENT MODEL

18. REFERENCES Lehninger Principles of Biochemistry by David L.Nelson,Michael M.Cox Fundamentals of Biochemistry – LIFE AT MOLECULAR LEVEL Donald Voet , Judith G. Voet , Charlotte W. Pratt The Early History of the Biochemistry of Muscle Contraction ;Andrew G.  Szent-Györgyi ( RESEARCH PAPER LINK- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2234565/#:~:text=A%20viscous%20protein%20was%20extracted,the%20rigor%20state%20of%20muscle )

19. THANK YOU