SPACI score report for 3sk4 in ASTRAL 2.06:

PDB Entry: 3sk4
SPACI score: 0.49
AEROSPACI score: 0.49

Experiment type: XRAY
Resolution: 1.85
R-factor: 0.177
PCK1 PROCHECK Ramachandran: 1
PCK2 PROCHECK Chi-1 angle: 2
PCK3 PROCHECK H-bonds: 2
WCK1 WHAT_CHECK Packing: -1.348
WCK2 WHAT_CHECK Ramachandran: -0.519
WCK3 WHAT_CHECK Chi angles: -0.492
WCK4 WHAT_CHECK Backbone: 2.876

Note: Here are links to pages about PROCHECK and WHAT_CHECK.

Here is the full WHAT_CHECK report on this protein (linked from the WHAT_CHECK site).