Transcript Document

HEMOGLOBIN AND MYOGLOBIN: NEW
PROPERTIES FROM QUATERNARY
STRUCTURE
Physiological functions
• Myoglobin stores
oxygen in muscles. It
releases oxygen only
when oxygen
concentration is very
low (hypoxia)
• Hemoglobin transfers
oxygen from lungs to
tissues. It releases
oxygen when oxygen
concentration is in
physiological range.
О2 is bound to heme group
Oxygen saturation curves for myoglobin (hyperbolic)
and hemoglobin (sigmoidal): different ability to
transfer oxygen
Lungs: both proteins are
saturated with oxygen.
Tissues:
- myoglobin is 90% saturated
(gives back only 10%)
- hemoglobin is 50%
saturated (gives back 50%)
QUATERNARY STRUCTURE
MATTERS
Myoglobin consists of single polypeptide
chain, while functional hemoglobin molecule
contains four polypeptide chains (which are
very similar to myoglobin ones)
Myoglobin
(single chain)
Hemoglobin
(one subunit)
Hemoglobin
(four subunits)
Binding of oxygen molecule by the
first subunit enhances oxygen
binding to other subunits
This feature is called cooperativity
THE CAUSE OF COOPERATIVITY
Subunits interact with each other
Interaction in more details
Oxygen binding leads to structural (conformational)
changes in binding site, which are transmitted to
neighboring subunits through contacts between
subunits
Binding of oxygen molecule by the first
subunit enhances oxygen binding to
other subunits
Structure determines ability for oxygen binding
Conformational (structural) changes in
hemoglobin molecule after oxygen binding
Summary
• Binding of the first oxygen molecule
changes structure of neighboring subunits
• These changes enhance oxygen binding
Hemoglobin: physiological
regulation
2,3-BISPHOSPHOGLYCERATE AND
COOPERATIVITY
2,3-BPG is produced from one of the glycolysis
intermediates
The presence of 2,3BPG indicates sites of
high energy
production and,
therefore, oxygen
demand
2,3-BPG binds to the central cavity of
hemoglobin molecule
Effects of 2,3-BPG:
• 2,3-BPG weakens oxygen binding.
Therefore:
• High 2,3-BPG in tissue → weak oxygen
binding → better oxygen supply
This plays role in adaptation to highlands and
intensive work
CLINICAL POINTS:
BINDING OF CO
CO binding disturbs cooperativity of oxygen binding
HEMOGLOBIN ISOFORMS:
- ADULT
- FETAL
Synthesis of different isoforms during embryonic
development
Fetal vs. adult hemoglobin
PHYSIOLOGICAL REGULATION OF
OXYGEN BINDING: EFFECTS OF PH AND
CO2
Effects of pH and CO2
Tissues with high
energy demand
(high glycolysis):
- high CO2
-low pH
Summary
• Proteins with quaternary structure may display
cooperative binding
• Cooperativity is caused by conformational changes in
the first protein subunit which lead to conformational
and binding rate changes in neighboring subunits
• Regulatory molecules usually change conformation and
therefore properties of protein
• This is the basis of physiological regulation of protein
activity
• In hemoglobin oxygen binding is regulated by 2,3-BPG,
CO2 and pH
• Different protein isoforms are differently regulated
NUCLEIC ACIDS
DNA and RNA contain nitrogen bases
Nucleotides vs. nucleosides
How is this
nucleoside /
nucleotide
called?
There are some other nitrogen
bases
• Alkaloids
• Products of nitrogen bases breakdown
Some bases are not included in nucleic
acids structure: alkaloids
H
caffeine
H
theophilline
theobromine
Nitrogen bases which are formed during
metabolism from adenine and guanine
hypoxanthine
xanthine
Uric acid
Elevation of uric acid causes gout
• Uric acid forms
insoluble salts
• Causes: increased
production OR
decreased
excretion
DNA contains minor (modified) bases:
regulation of gene expression by methylation
RNA contains minor bases:
recognition, stability, regulation
mRNA
tRNA
FUNCTIONS
ATP as energy carrier
high energy bond (macroergic
bond, high energy phosphate)
= good leaving group,
high transfer potential
(correct meaning)
Nucleotide moieties of coenzymes: coenzyme A
Nucleotide moieties of coenzymes: NAD
Nucleotide moieties of
coenzymes: FAD
Regulatory functions of cyclic nucleotides
cAMP has positive effect on
energy-production pathways
(glycolysis). One of the
mechanisms of caffeine
action is inhibition of cAMP
breakdown. This leads to
prolongation of cAMP
stimulatory action.
cGMP mediates muscle
relaxation caused by NO. Effect
of nitroglycerin on heart muscle
relaxation is mediated by cGMP
formation.
Summary
• Nucleotides consist of nitrogen base
(A,T,G,C,U) + (deoxy)ribose + phosphate
• Nucleotides are the building blocks of
nucleic acids (DNA, RNA)
• Nucleotides perform signaling functions
(cAMP, cGMP)
• Nucleotides play role in catalysis (parts of
coenzymes).
• Nucleotides are energy carriers (ATP, GTP)
NUCLEIC ACIDS: DNA
Nucleotides (in DNA or RNA) are
joined by phosphodiester bonds
Conventional order of
sequence description is from
5`- to 3`- end:
5` ATG 3`
DNA is a double helix
DNA STRUCTURE AND DRUGS
Intercalation – insertion between planar bases of
double helix
Intercalating drugs: bacteriostatics
proflavin
Intercalating drugs for cancer
cisplatin
Mechanism of intercalation
NUCLEIC ACIDS: RNA
Differences between RNA and DNA: pentose
Lack of OH-group makes DNA more
chemically stable: DNA is more suitable for
storing genetic information
RNA functions in protein synthesis:
ribosomal RNA perform catalytic
functions
RNA is the major structural component of ribosomal subunits
30S
rRNA (brown)
+ proteins
(blue):
rRNA:
50S
RNA functions in protein synthesis:
transfer RNA (tRNA)
Real conformation in 3D
RNA functions in protein synthesis:
messenger RNA (mRNA)
Other functions of RNA:
• Catalysis (ribozymes): ribosome, RNAse P,
hammerhead ribozyme.
• Regulation of gene expression (RNA
interference): small interfering RNAs
RNA as catalyst: ribozymes
RNase P plays role in:
- tRNA processing
- regulation of
transcription