BIO 311 Chapter Notes - Chapter 6: Multiple Sequence Alignment, Heterotetramer, Myoglobin
Quaternary (4°) Structure of Proteins
• Quatea stutue is the fial leel of potei stutue ad petais to
proteins that consist of more than one polypeptide chain - each chain is called a
subunit, the number of which can range from two to more than a dozen
• The hais a e idetial hoo-) or different (hetero-)
• Cool ouig eaples ae dies , ties , ad tetaes , of
polypeptide chains
• These polpeptide hais iteat ith oe aothe ooaletl ia
electrostatic attractions, hydrogen bonds, and hydrophobic interactions
• As a esult of these ooalet iteatios, sutle hages i stutue at oe
site on a protein molecule may cause drastic changes in properties at a distant
site - proteins that exhibit this property are called allosteric
• A lassi illustatio of the uatea stutue ad its effet o potei
properties is a comparison of hemoglobin, an allosteric prote
Hemoglobin
• Heogloi is a tetae, osistig of fou polpeptide hais, to α-chains and
to β-chains - in oligomeric proteins, the types of polypeptide chains are
designated with Greek letters
• The to α-hais of heogloi ae idetial, as ae the to β-chains
• The oeall stutue of heogloi is desigated as α β - a heterotetramer
• Both the α-hais ad the β-chains of hemoglobin are similar to myoglobin - the
α-hai is esidues log, the β-chain is 146 residues long (myoglobin is 153
residues long)
• Ma of the aio aids of the α-hai, the β-chain, and myoglobin are
homologous - that is, the same amino acid residues are in the same positions
• The hee goup is also the sae i ogloi ad heogloi
• Mogloi ids oe O oleule hile heogloi ids fou
• Both heogloi ad ogloi id O eesibly, but the binding of O2 to
hemoglobin exhibits positive cooperativity, whereas O2 binding to myoglobin does
not
Multiple Protein Sequence Alignment
• HBA, α-suuit; HBB, β-subunit; MB, myoglobin
• The ultiple seuee aliget illustates the high degree of
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conservation between the amino acid sequences
D94
H143 H146
Fig. 4-21, p. 107
Hemoglobin
• The oeall stutue of heogloi is that of a heteotetae ad is desigated
as αβ
• Both the α-hais ad the β-chains of hemoglobin are similar to myoglobin - and
all four polypeptide chains can bind O2 through the heme group
Hemoglobin - Positive Cooperativity
• O idig heogloi ehiits positie oopeatiit - this means
that the binding of one O2 molecule stimulates the binding of another
• The O-binding curve of myoglobin is hyperbolic while that of hemoglobin
is sigmoidal
• The shape of the heogloi idig ue idiates that the idig of
the first O2 molecule facilitates the binding of the second and so on -
cooperative binding
• Ipotat to ote that i spite of oopeatie idig, ogloi has a
higher O2 binding capacity than hemoglobin
Fig. 4-22, p. 107
Hemoglobin - Positive Cooperativity
hyperbolic
sigmoidal
Respiratory/Circulatory System
• Withi the lugs, ou ohi branch into thousands of thin
tubes called bronchioles
• The ohioles ed i uhes of ti oud ai sas alled
alveoli
• The aleoli osist of a epithelial lae ad etaellula ati
surrounded by a mesh of tiny blood vessels called capillaries
• Though a gas ehage poess, O oes fo the aleoli to
hemoglobin in erythrocytes travelling through the capillaries
• The O-rich blood travels to the heart through the pulmonary
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Document Summary
Multiple protein sequence alignment: hba(cid:1006), -su(cid:271)u(cid:374)it; hbb, -subunit; mb, myoglobin, the (cid:373)ultiple se(cid:395)ue(cid:374)(cid:272)e alig(cid:374)(cid:373)e(cid:374)t illust(cid:396)ates the high degree of conservation between the amino acid sequences. Hemoglobin - the bohr effect: i(cid:374) a(cid:272)ti(cid:448)el(cid:455) (cid:373)eta(cid:271)olizi(cid:374)g tissue, he(cid:373)oglo(cid:271)i(cid:374) (cid:396)eleases o(cid:1006)-and binds both. Co2 and h: i(cid:374) the al(cid:448)eoli of the lu(cid:374)gs, he(cid:373)oglo(cid:271)i(cid:374) (cid:396)eleases co(cid:1006) a(cid:374)d h+ a(cid:374)d (cid:271)i(cid:374)ds to. Hemoglobin - the bohr effect: the o(cid:1006) satu(cid:396)atio(cid:374) (cid:272)u(cid:396)(cid:448)es fo(cid:396) (cid:271)oth (cid:373)(cid:455)oglo(cid:271)i(cid:374) a(cid:374)d he(cid:373)oglo(cid:271)i(cid:374, the affi(cid:374)it(cid:455) of (cid:373)(cid:455)oglo(cid:271)i(cid:374) fo(cid:396) o(cid:1006) is u(cid:374)affe(cid:272)ted (cid:271)(cid:455) ph, ho(cid:449)e(cid:448)e(cid:396), at lo(cid:449)e(cid:396) ph, the affi(cid:374)it(cid:455) of he(cid:373)oglo(cid:271)i(cid:374) fo(cid:396) o(cid:1006) is sig(cid:374)ifi(cid:272)a(cid:374)tl(cid:455) (cid:396)edu(cid:272)ed. , releasing h: the presence of larger amounts of h+ as a result of co2 production favors the quaternary structure of deoxygenated hemoglobin - hence the affinity of hemoglobin for o2 is lowered, the hco(cid:1007) Hemoglobin - 2,3-bisphosphoglycerate (you do not need to remember the structure of bpg)
