| Summary: | 碩士 === 國立臺灣大學 === 分子醫學研究所 === 85 === The most significant indoor allergens are those of the house
dust miteswhich play a major role in the induction of asthma,
allergic rhinitisand allergic dermatitis. The predominant mite
species in Taiwan isDermatophagoides pteronyssinus. The past
finding suggested that the cDNAclone encoding Der p 5 allergen
produced a 132-residue polypeptide which has a putative
19-residue leader peptide and a 113-residue mature protein(Lin
et al., 1994). Here we report our structural studies of Der p 5
which is composed of 115-residue by recombinant DNA technology.
First, X-ray crystallography is used to explore the three-
dimensional structure of Der p 5. The large octahedral crystal
were obtained at areservoir solution with 5% PEG6K, 1mM CaCl2,
10 mM(NH4)2HPO4, and 0.1 M citric acid-Na2Hpo4 (pH 3.4), at 22
C. The crystal diffract 3A resolution, belong to the tetragonal
space group, P41212 or P43212. The cell dimensiona=b=113.5A,
c=234.3A. By self rotation function analysis, there are
significant2-, 3-, and 4-fold noncrystallographic axes in the
asymmetric unit and thenit suggested there are 96monomers in a
unit cell. Furthermore, using gel filtration chromatography,
dynamic light scattering, and electron microscope,we
surprisingly found that Der p5 is monomeric at neutral pH,
whereas it formspolymeric gilaments at low pH.Studies by
circular dichroism suggested that Der p 5 is a helical protein.
Theapplication of NEWCOLL and COILS programs predicted the C-
terminal residues ofDer p 5 as a coiled-coil a-helix. In
addition, the high content of chargedamino acid residues of Der
p 5, 23% negatives and 20% positive, implied that the
electrostatic interactions play a key role in protein
aggregation. Finally,the other allergrns form dust mite are also
analysises because it is believed that the coiled-coil a-helix a
is a high immunogenic structure motif. Besides Der p 5, some
non-enzymatic allergens (eg. Der p 2, Der p 7, Der f 2, Mag
29)contain the 4,3-hydrophobic repeat which could potential form
coiled-coils.Therefore the a-helical coiled=coils of these
allergens may play key roles in their immunogenicity.
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