Title : Crystal structure of the novel complex formed between
zinc alpha2-glycoprotein (
ZAG ) and
prolactin-inducible protein (
PIP ) from human seminal plasma
Abstract :
- This is the first report on the formation of a complex between zinc alpha2-glycoprotein ( ZAG ) and prolactin-inducible protein ( PIP )
- The complex was purified from human seminal plasma and crystallized using 20% polyethylene glycol 9000 and 5% hexaethylene glycol
- The structure of the complex has been determined using X-ray crystallographic method and refined to an R(cryst) of 0.199 (R(free)=0.239)
- The structure of ZAG is broadly similar to the structure of serum ZAG
- The scaffolding of PIP consists of seven beta-strands that are organized in the form of two antiparallel beta-pleated sheets, resulting in the formation of a sandwiched beta-sheet
- The amino acid sequence of PIP contains one potential N-glycosylation site at Asn77 , and the same is found glycosylated with four sugar residues
- The structure of the complex shows that the beta-structure of PIP is ideally aligned with the beta-structure of domain alpha3 of ZAG to form a long interface between two proteins
- The proximal beta-strands at the long interface are arranged in an antiparallel manner
- There are 12 hydrogen bonds and three salt bridges between ZAG and PIP
- At the two ends of vertical interface, two salt bridges are formed between pairs of Lys41-Asp233 and Lys68-Glu229
- On the perpendicular interface involving alpha1-alpha2 domains of ZAG and a loop of PIP , another salt bridge is formed
- The internal space at the corner of the L-shaped structure is filled with solvent molecules including a carbonate ion
- The overall buried area in the complex is approximately 914 A(2) , which is considerably higher than the 660 A(2) reported for the class I major histocompatibility complex structures