Experimental observations:

0) Native mmcp7 monomer, after activation by release of pro-part, 
   forms an active tetramer, which then dissociates into inactive,
   but uncleaved dimers and monomers within one day;

1) Heparin (glycerol) is not essential for forming tetramer, although it
   does increase the final activity for a factor of 3.

2) The tetramer formation/proteolytic activity is pH depdendent - maximum
   at pH ~5.

3) Mutant W14L does not form dimers/tetramers.

4) Mutant W206L forms some dimers/tetramers, but very unstable at 36 degrees C.

5) W14, W206, W126, W12 are the hydrophobic cluster.


Questions:

1) Does the native mmcp-7 form a dimer to the same degree as the W14L mutant?

2) Does heparin interact with the tetramer or dimer?

3) How many monomers in the tetramer are proteolytically active?
   This could perhaps be done by generating an inactive monomer
   (active site mutant, say Ser-->Ala) and then doing mixing experiments 
   with different ratios of the native mMCP-7 and active site mutant.

4) Is tetramer formation dependent on salt concentration?

5) Does the pH dependence shown in the Fig. reflect the dependence
   of tetramer concentration or activity on pH?

6) PF4 does not have the x-ray structure available - it is just a model
   based on the monomer structure and proteolysis data for the tetramer.

7) Why were the other two Trp in the cluster not mutated?


Things to do for us:

1) Use the Jernigan program to define hydrophobic clusters on mMCP-7.

2) See how to fit the data by the independently calculated monomer, dimer,
   tetramer models. Or how to get those models consistent with the data.
