The role of secondary structure in the entropically driven amelogenin self-assembly.
Amelogenin, the major extracellular enamel matrix protein, plays critical roles in controlling enamel mineralization. This generally hydrophobic protein self-assembles to form nanosphere structures under certain solution conditions. To gain clearer insight into the mechanisms of amelogenin self-assembly, we first investigated the occurrences of secondary structures within its sequence. By applying isothermal titration calorimetry (ITC), we determined the thermodynamic parameters associated with protein-protein interactions and with conformational changes during self-assembly. The recombinant porcine full length (rP172) and a truncated amelogenin lacking the hydrophilic C-terminal (rP148) were used. Circular dichroism (CD) measurements performed at low concentrations (<5 microM) revealed the presence of the polyproline-type II (PPII) conformation in both amelogenins in addition to alpha-helix and unordered conformations. Structural transition from PPII/unordered to beta-sheet was observed for both proteins at higher concentrations (>62.5 microM) and upon self-assembly. ITC measurements indicated that the self-assembly of rP172 and rP148 is entropically driven (+DeltaS(A)) and energetically favorable (-DeltaG(A)). The magnitude of enthalpy (DeltaH(A)) and entropy changes of assembly (DeltaS(A)) were smaller for rP148 than rP172, whereas the Gibbs free energy change of assembly (DeltaG(A)) was not significantly different. It was found that rP172 had higher PPII content than rP148, and the monomer-multimer equilibrium for rP172 was observed in a narrower protein concentration range when compared to rP148. The large positive enthalpy and entropy changes in both cases are attributed to the release of ordered water molecules and the associated entropy gain (due to the hydrophobic effect). These findings suggest that PPII conformation plays an important role in amelogenin self-assembly and that rP172 assembly is more favorable than rP148. The data are direct evidence for the notion that hydrophobic interactions are the main driving force for amelogenin self-assembly.
Lakshminarayanan
Rajamani
R
University of Southern California, School of Dentistry, Center for Craniofacial Molecular Biology, Los Angeles, California 90033, USA.
Fan
Daming
D
Du
Chang
C
Moradian-Oldak
Janet
J
D053523:Amelogenin / Q000737:chemistry*; D000818:Animals; D002942:Circular Dichroism; D004305:Dose-Response Relationship, Drug; D019277:Entropy; D004926:Escherichia coli / Q000378:metabolism; D008027:Light; D010455:Peptides / Q000737:chemistry; D011487:Protein Conformation; D025941:Protein Interaction Mapping; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D013552:Swine; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
D053523:Amelogenin; D010455:Peptides; D011994:Recombinant Proteins; D014867:Water
Curr Top Dev Biol. 2006;74:57-115
16860665
J Biol Chem. 2005 Jan 28;280(4):2682-90
15550396
J Mol Biol. 1995 Oct 6;252(5):633-42
7563079
Biochemistry. 2001 Dec 4;40(48):14376-83
11724549
Biophys J. 2005 Nov;89(5):3332-6
16100270
Eur J Biochem. 2001 Feb;268(4):1118-28
11179978
Proteins. 2006 Feb 1;62(2):461-9
16284958
Biomaterials. 2007 Jul;28(19):3034-42
17382381
J Biol Chem. 2006 Jul 28;281(30):21173-82
16707492
Biochemistry. 1995 Mar 28;34(12):3873-7
7696249
Biophys Chem. 1988 Aug;31(1-2):143-6
3233285
J Struct Biol. 2005 Sep;151(3):239-49
16125972
Science. 2005 Mar 4;307(5714):1450-4
15746422
Biochem J. 1994 Jan 15;297 ( Pt 2):249-60
8297327
Science. 1994 Feb 11;263(5148):777-84
8303294
Chem Rev. 2006 May;106(5):1877-97
16683759
Matrix Biol. 2001 Jul;20(4):243-50
11470400
Proc Natl Acad Sci U S A. 2003 Sep 2;100(18):10258-62
12930900
J Dent Res. 2002 Jan;81(1):69-73
11820371
Biochemistry. 1994 Nov 1;33(43):12741-5
7947677
J Biol Chem. 1987 Nov 15;262(32):15696-701
3316206
Eur J Biochem. 2001 Dec;268(24):6600-6
11737214
J Biol Chem. 2002 Nov 22;277(47):45572-8
12324465
J Phys Chem B. 2005 Dec 15;109(49):23611-7
16375338
J Struct Biol. 1994 Mar-Apr;112(2):103-9
8060728
Biochim Biophys Acta. 2000 Nov 23;1508(1-2):69-85
11090819
Matrix Biol. 2001 Sep;20(5-6):293-305
11566263
J Struct Biol. 2005 Feb;149(2):182-90
15681234
J Am Chem Soc. 2004 Dec 22;126(50):16544-52
15600359
Bone. 2004 Jul;35(1):4-10
15207735
Calcif Tissue Int. 1994 Jan;54(1):69-75
8118757
Proc Natl Acad Sci U S A. 1983 Dec;80(23):7254-8
6139813
Proc Natl Acad Sci U S A. 2000 May 9;97(10):5129-34
10805776
Eur J Oral Sci. 2006 May;114 Suppl 1:59-63; discussion 93-5, 379-80
16674664
Methods Mol Biol. 2004;261:35-54
15064448
Proteins. 1999 Sep 1;36(4):400-6
10450081
J Mol Biol. 1993 Jan 20;229(2):472-93
8429558
Biochemistry. 1998 Jul 14;37(28):10223-30
9665729
Matrix Biol. 2001 Sep;20(5-6):273-92
11566262
Arch Oral Biol. 1997 Mar;42(3):235-42
9188994
Matrix Biol. 2002 Mar;21(2):197-205
11852235
Biopolymers. 1991 Nov;31(13):1463-70
1814498
J Dent Res. 1996 Oct;75(10):1735-41
8955667
Proc Natl Acad Sci U S A. 1999 Dec 7;96(25):14183-5
10588672
J Struct Biol. 2006 Feb;153(2):176-87
16413789
J Biomol Struct Dyn. 1998 Jun;15(6):1029-37
9669549
Science. 2005 Jul 8;309(5732):275-8
16002612
J Biol Chem. 2001 Aug 24;276(34):31871-5
11406633
Int J Pept Protein Res. 1996 Oct;48(4):328-36
8919053
Biophys J. 2001 Sep;81(3):1547-54
11509367
J Biol Chem. 1988 Jul 25;263(21):10517-23
3392022
J Biochem. 1993 Jan;113(1):55-60
8454575
Chirality. 2002 Nov;14(10):782-92
12395395
J Dent Res. 2006 Sep;85(9):775-93
16931858
J Struct Biol. 1999 Jun 30;126(3):270-99
10441532
Cells Tissues Organs. 2005;181(3-4):202-18
16612086
Biochemistry. 1997 Jul 8;36(27):8413-21
9204889
Biochemistry. 1986 Aug 26;25(17):4879-87
3768319