<ng-container matColumnDef="fifthColumn">
    <mat-header-cell *matHeaderCellDef mat-sort-header [ngClass]="{columnsData['fifthColumn'].size:true, shouldLock:shouldLockChecker}" > {{columnsData['fifthColumn'].name}} </mat-header-cell>
    </ng-container>


where --> columnsData['fifthColumn'].size is a property, that im taking from an object and i want to be always added to the ng class
where --> shouldLock is a string, that i want to add in the ngClass upon some events