SPACI score report for 3g21 in ASTRAL 2.05:

PDB Entry: 3g21
SPACI score: 1.15
AEROSPACI score: 1.15

Experiment type: XRAY
Resolution: 0.9
R-factor: 0.124
PCK1 PROCHECK Ramachandran: 1
PCK2 PROCHECK Chi-1 angle: 1
PCK3 PROCHECK H-bonds: 2
WCK1 WHAT_CHECK Packing: 0.458
WCK2 WHAT_CHECK Ramachandran: 1.869
WCK3 WHAT_CHECK Chi angles: 1.126
WCK4 WHAT_CHECK Backbone: 1.457

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).